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An English Essay on the Importance of Water for the Students

Without water there cannot be life on our planet, that is to say on earth. Because every living organism needs water, and therefore having a good understanding and care for the water is a must for all of us. Hence, students should write an essay discussing the importance of water in the English language.

Writing an essay on such a topic opens a series of good ideas in the mind of the students regarding the role that water plays in our lives, and it can also make the students aware of the importance of water.

Also, if you wish to write an English essay on the topic My aim in life you may find this link helpful My Aim in Life Essay in English for Students | Easy Essay on My Aim in Life (vedantu.com)

Advantages of Writing an Essay on the Importance of Water.

Writing an essay on any topic helps the students be good writers, and the same goes for the topic of, Importance of water, but there are quite a few more advantages to writing the essay.

One of the most important things for everyone is to express oneself, and the practice of doing so must be given to the child from a very young age. And writing an essay helps the students in this very important thing.

For writing a good essay on any topic, the students must have a good understanding of the subject of the essay. And hence, writing an essay on the Importance of water, helps the students in learning about the value of water, not just our lives, which is to say humans, but the life of the whole planet.

In his famous play Hamlet Shakespeare writes, Brevity is the soul of wit, meaning being short or concise is very important in speech, or shortness of words is the essence of intelligence. The same rule applies in writing the essay, and doing as clear an understanding of the topic at hand is required as possible. And hence composing an essay on the importance of water helps the students understand the same.

One of the most important gifts that humans are blessed with is the gift of language, and this gift has to be used effectively. Writing an essay helps the students in learning the methods of using the language in such a manner that it makes everything clear to the reader. A good essay does not only touch the heart of the readers but it opens the mind of the reader, it can move them, that is to say, if a good essay is written on the importance of water it can make the readers aware about the same, and not just aware but also careful about using the water.

Water means Life. Water is a prime natural resource. It is a basic need for humans and a precious asset that living beings have. Water is equally vital for the survival of the plant and animal kingdoms. Soil needs water for sustaining plants. The water cycle is essential for ecological balance too. Though a big portion of the Earth is covered with water, only a small portion of it can be used for various human activities. So we need to be judicious and rational, regarding the usage of water.

Why is water important for our bodies?

Water is important for our body for the following reasons. 

 Above 70% of our body contains water so it is pivotal for the human race to survive. 

Water helps in regulating our body temperature. 

 Water helps in the digestion of solid food. 

It also keeps our skin healthy and hydrated. 

Water helps in excreting waste from our body through sweat, urination, and defecation. So replenishing the water in our body is essential to prevent dehydration.

Drinking water also helps in reducing calories and maintaining body weight because it can increase the rate of metabolism.

Water consumption lubricates the joints, spinal cord, and tissues.

Importance of Water

All living organisms, plants, animals, and human beings contain water. Almost 70% of our body is made up of water. Our body gets water from the liquids we drink and the food we eat. Nobody can survive without water for more than a week. All plants will die if they do not get water. This would lead to the death of all the animals that depend on plants for their food. So the existence of life would come to an end.

Role of Water In Life Processes

Water plays an important role in most of the life processes by acting as a solvent. The absorption of food in our body takes place in solution form with water as the solvent. Also, many waste products are excreted in the form of solutions through urine and perspiration. 

Water helps in regulating our body temperature. In hot weather, we drink a lot of water. This maintains our body temperature. Also, water evaporates from the surface of our body as sweat. This takes away heat and cools the body. 

Water is essential for plants to grow. Plants need water to prepare food. They also absorb dissolved nutrients from the soil through their roots. 

Aquatic plants and animals use the nutrients and oxygen dissolved in water for their survival. 

Uses of Water In Everyday Life

Water is used for drinking, washing, cooking, bathing, cleaning, in our day-to-day life.

It is used to generate electricity in hydroelectric power stations.

Water is used for irrigating fields and in the manufacture of various products. 

Other Uses of Water

Water serves as a means of transportation for goods and people.

It provides a medium for recreational sports such as swimming, boating, and water skiing. 

Water is also used to extinguish fires. 

Importance of Oceans

Oceans are of immense use to man. They are useful in many ways, directly and indirectly. They not only play a significant role in the climate of adjoining countries but also serve mankind in many ways. They are a storehouse of several resources. 

An ocean is a major source of water and forms a major part of the water cycle. Oceans contribute water vapor to the atmosphere and we get the same in the form of precipitation.

The oceans are the biggest storehouse of edible forms of marine food, fish being most important. In addition to food, sea animals provide other products like oil, glue, etc.

Oceans have enormous mineral and chemical wealth. A variety of dissolved salts like sodium chloride (common salt), magnesium chloride, and potassium chloride are found in plenty in the oceans.

Oil and gas are important fuels obtained from oceans.

Importance of Lakes and Rivers

Economic and industrial development

Water storage

Hydroelectric power generation

Agricultural purposes

Modern multipurpose dams

Source of food

Source of minerals

Tourist attractions and health resorts

Rivers provide fresh drinking water

Ports can be built on them as they form good natural harbors 

Major Concerns

Although our planet Earth is covered with 71% percent of water and 29% of the land, the fast-growing contamination of water is affecting both humans as well as marine life. The unequal distribution of water on the Earth and its increasing demand due to the increasing population is becoming a concern for all. 

Water pollution makes it difficult for marine animals to sustain themselves.

Covering over 71% of Earth’s surface, water is undoubtedly the most precious natural resource that exists on our planet. Without the seemingly invaluable compound comprising Hydrogen and Oxygen, life on Earth would be non-existent. 

We are slowly but harming our planet at a very alarming rate.

Characteristics of a Good Essay.

It must be brief: As pointed out earlier, a good essay must be short, and also to the point. So, if students are writing an essay on the importance of water it must only deal with the water, and anything which does not directly serve the purpose must be excluded.

Must cover the whole topic: Though it may seem a little contradicting to the first point, what is meant by covering the whole topic is that the maximum number of aspects dealing with the importance of water must be covered in this essay. For instance, water is important for all living organisms and not just humans, and so the same has to be covered in one or the other way in the essay on the importance of the water.

Must be to the point: The essay must remain true to the central idea of the topic, which is the importance of water in this case. Hence, almost all the sentences written in the essay must serve the main topic in one or another way. And also, writing should not be vague or ambiguous, or illogical.

Human beings should realize how important and precious water is. At the individual level, you can be more responsible and avoid wasting water so that our future generation can make the best use of this natural resource abundantly.

FAQs on Importance of water

1. Why is water important?

Water is important because it sustains all living organisms on Earth.

2. How is ocean water useful to Mankind?

Ocean water is useful to mankind in the following ways.

Oceans are a major source of water through the water cycle. 

Oceans have direct control over the climate.

Oceans are the biggest storehouse of marine food.

Oceans have enormous mineral and chemical wealth.

3. How is water important for our Body?

Water helps to carry nutrients and oxygen to each and every cell of our body. It helps in digestion. It keeps our skin healthy and hydrated. Water consumption lubricates the joints, spinal cord, and tissues.

4. What are the uses of water in our Daily Life?

Water is used for drinking, bathing, cooking, cleaning, and irrigation of crops and manufacturing various products.

5. Why should I use the essay provided by Vedantu on the Importance of water?

The essay that Vedantu provides on the topic of the Importance of water is prepared by expert teachers, for the students of the English language. And hence this essay can be used by the students as an outline or an example of the essay on the Importance of water, it does not necessarily mean that the students have to copy it completely, but it serves the purpose of guiding the students in attempting the essay. Furthermore, the essay is completely free for download for all the students and also it is available in a PDF file format.

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Essay on Water | Water Essay for Students and Children in English

February 13, 2024 by Prasanna

Essay on Water in English: Water, the very reason for the existence of living beings on earth, constitutes of more than 70% of the planet. Water is that magical liquid, that provides life to animals, plants, trees, bacteria and viruses. Water is the very reason why earth can support life and other planets cannot.

Up to 60% of the human body is made up of water. While there is an abundance of water on the planet, not everything can be consumed by human beings and animals. It is unfortunate that only 3% of the water on earth is freshwater, which is portable and safe to consume.

You can read more  Essay Writing  about articles, events, people, sports, technology many more.

Hence, when such a valuable resource is scarce and non-renewable, it becomes of utmost Importance of Water judiciously.

Long and Short Essay on Water in English for Students and Children

In the article, we have provided a 600-word essay on water for kids, students, and schoolchildren for their usage in assignments, tests, and project work. We have also provided a 200-word essay on water for kids to use in exams and tests and learn everything about the water.

Long Essay on Water in English

Water, the pivotal ingredient in the essence of life, is the most important non-renewable resource, other than oxygen, for life to exist and thrive on our planet. Water which makes up almost one-third of the face of the planet has only 2.75% to 3.1% of fresh after that can actually be used by human beings, animals and plants.

This small percentage of fresh water is used by all living beings for their growth and survival. Plants and trees use it to for photosynthesis to grow. Animals and human beings use water to drink and bathe every day. Hence, judicious use of after should be followed since water is non-renewable and depleting at an ever-increasing rate. At this rate, water will become redundant for future generations, which is to say that life will become non-existent on earth. Experts say that those unimaginable days are not very far from us if we don’t use water with responsibility.

Water that is present in oceans and seas, that is saltwater, is not consumable by human beings and land animals. But this water acts as a lifeline for certain aquatic life.

There are various types of water resources, both potable and non-potable, in the world namely, surface water, rainwater, groundwater, well water, lake water, river water, glaciers, snow etc. All these water bodies form the main source of water on the planet. And to keep these water bodies replenished all the time, a healthy water cycle should be maintained in our ecosystem. Any little disturbance in the water cycle can lead to global warming, floods and droughts.

Usages of water

• Human beings use water for drinking bathing, cooking, washing, watering etc.
• Industries and factories use water for manufacturing purposes
• Animals use water for drinking and bathing
• Plants and trees use water to grow and produce food
• Farmers use water to cultivate the land and fulfil the population hunger
• Power plants and nuclear plants use water to produce energy and power

Why is Water Important for the Human Body?

• More than 70% of our body is made up of water. Without it, the human race will not survive
• Water in our body helps in regulating body temperature
• It keeps our organs and tissue moist and functioning
• It helps in digestion and breaking down of the food we take inside our bodies
• It keeps our skin healthy and nutritious

Scientists and engineers are working on projects and research, from many years, to convert saltwater into freshwater. If they succeed in doing that, then water will not be scarce anymore, but nevertheless, people should learn to use water judiciously, because we never know what nature might throw at us if we play with it. But till then, the only way out to survive is to use water very irresponsibly and strategically.

It is also predicted that the next world war will be fought for water. The symptoms of that are already being seen in the world nowadays, with examples like India and Pakistan fight over the Indus river, Turkey, Syria and Iraq fighting over Tigris-Euphrates river water, Karnataka and Tamil Nadu fighting over Kaveri river in India. These symptoms, if not taken care now itself, will easily lead to world war having catastrophic effects on humankind.

Before all these leads to the extinction of mankind, all the governments of different countries, people, businesses and organisation should come together and formulate proper policies and laws for responsible usage of water in the future.

Short Essay on Water in English

We have provided a 150 to 200 words essay on water which can be used by school students and children for their assignments and projects.

Water, the life-saving universal solvent is the most important element for the existence of living beings on earth.

Water is usually found in three states of matter, namely liquid, solid and gas. All three forms of water are important for the survival of the human race. Water, being a non-renewable resource is depleting at a very faster rate without any source of replenishment. The only way drinking water can be replenished and regenerated is through a healthy water cycle in the atmosphere. And for this water cycle to be maintained well, human beings need to learn to use natural resources like forest, coal and natural gas efficiently without harming the cycle of life.

Since water supports all forms of life, from surface animals and plant to aquatic plant and animals, the water resource belongs to every being on this plant and human beings should not be selfish in their greed for the usage of water.

The unplanned building of damns and man-made reservoirs, and being a thorn in the natural way of life has all affected the actual cycle of water. This has lead to massive drought and floods in various parts of the world.

All human beings should come together and join hands to use water efficiently and not indulge ourselves in the natural cycle of life and let nature thrive on their own.

10 Lines on Water Essay in English

• Water is the reason why life exists and grows on earth
• 70% of earth’s surface is made of water out of which only 3% is freshwater is for human consumption
• Water supports all forms of life on the planet
• Human beings use water for drinking, bathing, washing, in agriculture, industries and factories
• More than 60% of the human body is made up of water
• Animals use water for drinking and bathing purposes
• Plants, trees and various other living beings use water for its growth and survival
• It is predicted that the next world war will be fought for water if man does not learn how to use it judiciously
• The human beings need to learn to use water responsibly since it is a non-renewable resource
• Governments of all countries should come together to form policies and laws that forbid people from wasting water unnecessarily

FAQs on Essay on Water

Question 1. How much of the earth’s surface is made up of water?

Answer: More than 70% of the earth’s surface is made up of water out of which only 3% is potable freshwater

Question 2. Can water be manufactured?

Answer: As of now, it is not possible, but water can be recycled and reused after proper chemical treatments

Question 3. What are the sources of water?

Answer: Rivers, lakes, glaciers and groundwater table are some of the sources of water on earth

Question 4. Which is the biggest water body in the world?

Answer: Pacific ocean is the biggest water body in the world. Also, the Nile River is the largest source of freshwater in the world.

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Essay on Water

Here we have shared the Essay on Water in detail so you can use it in your exam or assignment of 150, 250, 400, 500, or 1000 words.

You can use this Essay on Water in any assignment or project whether you are in school (class 10th or 12th), college, or preparing for answer writing in competitive exams. 

Topics covered in this article.

Essay on Water in 150-250 words

Essay on water in 300-400 words, essay on water in 500-1000 words.

Water is a vital resource that sustains all forms of life on Earth. It covers about 70% of the planet’s surface, and its availability is essential for various human activities, ecosystems, and agriculture.

Water plays a crucial role in maintaining the balance of nature. It supports biodiversity, provides habitat for aquatic species, and ensures the survival of ecosystems. Additionally, water is essential for agriculture, enabling the growth of crops and the sustenance of livestock.

However, water scarcity and pollution have become significant challenges. Rapid population growth, industrialization, and climate change have put immense pressure on water resources. Many regions face water shortages, leading to social, economic, and environmental consequences.

Water pollution is another critical issue. Industrial discharge, agricultural runoff, and improper waste disposal contaminate water bodies, affecting both human health and aquatic life. It is crucial to implement sustainable water management practices, promote conservation efforts, and invest in water treatment infrastructure.

Education and awareness are key in fostering responsible water use. Individuals can contribute by conserving water, practicing efficient irrigation methods, and avoiding the contamination of water sources.

In conclusion, water is a precious resource that sustains life and ecosystems. The challenges of water scarcity and pollution require collective action to ensure its availability and quality. By implementing sustainable practices, promoting conservation, and raising awareness, we can protect and preserve this invaluable resource for future generations.

Water is a fundamental resource that is essential for all forms of life on Earth. It covers approximately 70% of the planet’s surface, playing a crucial role in supporting ecosystems, agriculture, and human activities.

Water is vital for the survival of living organisms and the maintenance of ecological balance. It provides habitat for a wide range of plants and animals, supporting biodiversity and contributing to the overall health of ecosystems. Water bodies, such as rivers, lakes, and oceans, serve as crucial habitats and breeding grounds for numerous species.

In agriculture, water is essential for crop irrigation and livestock sustenance. Farmers rely on water to nourish their crops and ensure food production. Additionally, water plays a critical role in the transport of nutrients within plants, enabling their growth and development.

Water is also crucial for human activities and economic development. It is used in households for drinking, cooking, and sanitation purposes. Industries depend on water for manufacturing processes, cooling systems, and energy production. Furthermore, water serves as a transportation medium for goods and people, facilitating trade and commerce.

However, the availability and quality of water face significant challenges. Rapid population growth, urbanization, and climate change exert pressure on water resources. Many regions around the world experience water scarcity, leading to social, economic, and environmental implications. The unequal distribution of water resources exacerbates these challenges, with some areas facing severe water shortages.

Water pollution is another pressing issue. Industrial discharge, agricultural runoff, and improper waste disposal contaminate water bodies, negatively impacting aquatic ecosystems and human health. Waterborne diseases and the degradation of aquatic habitats are direct consequences of water pollution.

Addressing these challenges requires sustainable water management practices. Conservation efforts, such as rainwater harvesting and efficient irrigation techniques, can help preserve water resources. Investment in water treatment infrastructure is crucial to ensure the provision of clean and safe drinking water to communities. Moreover, raising awareness about water conservation and pollution prevention is vital in fostering responsible water use among individuals and industries.

In conclusion, water is a precious resource that sustains life, ecosystems, and human activities. The challenges of water scarcity and pollution necessitate collective action and sustainable water management practices. By valuing water, implementing conservation measures, and raising awareness about responsible water use, we can ensure the availability and quality of water for future generations.

Title: Water – The Essence of Life

Introduction :

Water is the elixir of life, a precious resource that is vital for the existence of all living organisms on Earth. Covering about 70% of the planet’s surface, water is found in oceans, rivers, lakes, and underground reservoirs. It plays a fundamental role in sustaining ecosystems, supporting agriculture, meeting human needs, and shaping the landscape. This essay explores the significance of water, its diverse uses, the challenges it faces, and the importance of responsible water management for the well-being of our planet and future generations.

Importance of Water

Water is essential for the survival and well-being of all living organisms. It serves as a universal solvent, enabling chemical reactions that are crucial for life processes. Water is involved in cellular functions, temperature regulation, nutrient transportation, and waste removal in living systems. In addition to its biological importance, water also plays a critical role in maintaining ecological balance. It provides habitats for countless species, supports biodiversity, and influences the functioning of ecosystems.

Water for Agriculture

Agriculture is heavily dependent on water for crop cultivation and livestock sustenance. Irrigation systems deliver water to fields, ensuring the growth and productivity of crops. Water is essential for germination, photosynthesis, and the transport of nutrients within plants. Livestock farming relies on water for drinking, cleaning, and maintaining proper hygiene conditions. Adequate water supplies are essential for the health and well-being of both plants and animals in agriculture.

Water for Human Needs

Water plays a vital role in meeting various human needs. Access to clean and safe drinking water is crucial for maintaining human health and preventing waterborne diseases. Water is used for cooking, food preparation, and sanitation, ensuring proper nutrition and hygiene. Adequate sanitation facilities, including toilets and wastewater treatment systems, rely on water to prevent the spread of diseases and maintain public health. Moreover, water is used in industries for manufacturing processes, cooling systems, and energy production.

Challenges of Water Scarcity

Water scarcity is a pressing global challenge, particularly in regions facing population growth, urbanization, and climate change. Unequal distribution, overexploitation of water resources, and inefficient water management contribute to the scarcity of water. This scarcity can lead to social, economic, and environmental consequences. Reduced water availability hampers agricultural productivity, jeopardizes livelihoods, and triggers conflicts over water rights. Addressing water scarcity requires sustainable water management practices, water conservation efforts, and investments in water infrastructure.

Water Pollution and Conservation

Water pollution poses a significant threat to water resources and ecosystems. Industrial discharge, agricultural runoff, improper waste disposal, and the use of chemicals contaminate water bodies, compromising water quality. This pollution has detrimental effects on aquatic life, threatens biodiversity, and poses health risks to humans. Waterborne diseases, such as cholera and dysentery, are direct consequences of water pollution. To combat water pollution, stringent regulations must be implemented to control industrial and agricultural activities that contribute to pollution. Proper wastewater treatment systems and waste management practices are essential to preserve water quality.

Water conservation plays a pivotal role in ensuring sustainable water use. Rainwater harvesting, efficient irrigation techniques, and public awareness campaigns promote responsible water consumption. Governments, communities, and individuals must work together to reduce water wastage, encourage water reuse, and protect water sources from pollution.

Conclusion :

Water is a precious and finite resource that is vital for all forms of life on Earth. Its significance extends beyond meeting basic needs and supporting ecosystems; water plays a critical role in shaping our planet. The challenges of water scarcity and pollution necessitate collective action and responsible water management practices. By valuing water, promoting conservation efforts, and raising awareness about responsible water use, we can ensure the availability and quality of water for future generations. It is our collective responsibility to protect and preserve this invaluable resource, safeguarding the well-being of our planet and all its inhabitants.

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Essay about water 1 (100 words).

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Short Essay on Importance of Water 2 (200 words)

Essay on important uses of water 3 (300 words), introduction, different uses of water:.

• Drinking and Hydration: The most basic and crucial use of water is for drinking and staying hydrated. Water is essential for maintaining the body's fluid balance, regulating body temperature, and facilitating the transportation of nutrients and oxygen to cells.
• Agriculture: Water is indispensable for agricultural practices. Irrigation systems rely on water to provide crops with the necessary moisture for growth. It is estimated that about 70% of global freshwater usage goes towards agriculture, highlighting its crucial role in food production.
• Domestic Use: Water is used extensively for various domestic purposes, such as cooking, cleaning, bathing, and sanitation. It is vital for personal hygiene and maintaining a clean living environment.
• Industry: Water plays a significant role in various industrial processes. It is used for cooling machinery, generating steam, and cleaning equipment. Industries such as manufacturing, power generation, and chemical production rely heavily on water for their operations.
• Recreation and Tourism: Water-based recreational activities, such as swimming, boating, and fishing, are popular leisure pursuits for many people.

Essay About Water Cycle 4 (400 words)

Why is the water cycle important, important sources of water, water as essential part of our life - essay 5 (500 words), water – an essential part of the human body, water – vital for plant growth, water – habitat for marine creatures, essay about water 6 (600 words), significance of water, a world without water.

Frequently Asked Questions

Can water be manufactured?

No, water cannot be manufactured. While various processes can produce purified or desalinated water, the actual creation of water molecules from scratch is not possible in a laboratory or industrial setting.

Which is the biggest water body in the world?

The Pacific Ocean holds the distinction of being the largest water body on Earth. Spanning approximately 63.8 million square miles (165.2 million square kilometers), it encompasses vast expanses of water, making it the largest and deepest ocean globally.

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Essay on Importance of Water in Our Life

Students are often asked to write an essay on Importance of Water in Our Life in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

Let’s take a look…

100 Words Essay on Importance of Water in Our Life

Introduction.

Water is a vital component of life. It’s everywhere, from the food we eat to the air we breathe.

Health Benefits

Water keeps our bodies running. It helps transport nutrients, regulate body temperature, and remove waste.

Role in Nature

Water is crucial for plants and animals. It helps plants grow and provides a habitat for aquatic life.

Water is essential for life and our wellbeing. We must value and conserve it for a sustainable future.

250 Words Essay on Importance of Water in Our Life

The essence of life.

Water, a simple molecule consisting of two hydrogen atoms bonded to one oxygen atom, plays an indispensable role in our lives. It is the lifeblood of the environment, essential for the survival of all living organisms.

The Biological Significance

Water makes up approximately 60% of the human body, serving as a medium for biochemical reactions, aiding in digestion, and regulating body temperature. It transports nutrients and oxygen to cells, lubricates joints, and protects sensitive tissues. Without water, these vital processes would cease, leading to life-threatening consequences.

Environmental Impact

Beyond individual organisms, water is integral to ecosystems. It supports biodiversity, with different species adapted to various aquatic environments. Rivers, lakes, and oceans are teeming with life, each contributing to the balance of nature. The water cycle also plays a key role in weather patterns and climate regulation.

Societal Implications

Water is a critical resource for societal development. It is used in agriculture for food production, in industries for manufacturing goods, and in homes for daily chores. Clean drinking water is a fundamental human right, yet many regions still struggle with water scarcity, emphasizing the need for sustainable water management.

500 Words Essay on Importance of Water in Our Life

Water is a fundamental resource that is intricately woven into every facet of human life. It is a life-sustaining element, vital for the survival of all organisms on Earth. Its importance extends beyond quenching thirst and facilitating hygiene, to societal and developmental realms, contributing significantly to the global economy and food security.

Water as a Life-Sustaining Element

The human body is composed of about 60% water, serving as a medium for various biochemical reactions. It aids in digestion, absorption of nutrients, regulation of body temperature, and excretion of waste substances. Dehydration can lead to serious health problems, highlighting the importance of regular water intake.

Water in Agriculture and Food Security

Agriculture is the largest consumer of freshwater, accounting for nearly 70% of all water withdrawals globally. Water is essential for crop growth and livestock rearing, playing a pivotal role in ensuring food security. With climate change exacerbating water scarcity, efficient water management strategies in agriculture are crucial for sustainable development.

Economic Significance of Water

Societal and cultural importance of water.

Water has profound societal and cultural significance. It is central to many religious rituals and ceremonies, symbolizing purity and life. Moreover, water bodies have shaped human settlements, with many ancient civilizations flourishing around rivers and coasts. Today, they continue to influence urban planning and architecture.

Water and the Environment

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Essay on Water Conservation: Samples in 150, 200, 250 Words

• Updated on  
• May 8, 2024

What makes you curious to write an essay on water conservation? This life-saving resource is essential for all forms of life on Earth. Water is the essential natural resource present on Earth. Out of the total water present on Earth, 97.5% is salt water and 2.5% is fresh water. 70% of the human body is made of water. But, with the growing population , and climatic crisis , we are facing the urgent need to conserve water.

Water conservation is a hot topic, if you need a sample essay on water conservation then, you are at the right place. In this blog post, we have covered essays on water conservation in 100, 200, and 250 words. Further we are also providing a sample piece of writing on essay on water conservation. So, stay tuned and read further to get some ideas about water conservation!

Table of Contents

• 1 Essay on Water Conservation in 100 Words
• 2 Essay on Water Conservation in 200 Words
• 3.1 Water Scarcity
• 3.2 Ways to Conserve Water
• 4 Short Essay on Water Conservation

Also Read: World Water Day

Essay on Water Conservation in 100 Words

Water is crucial for all components of life which makes it a necessary resource for day-to-day activities. We use water for domestic activities like cooking, bathing, drinking, washing, etc. So, ultimately the consumption of water is very high. This makes it necessary to conserve water. Just as air, water is also important for life. Besides, water consumption, water pollution, and water scarcity are also some of the major water-related issues that need attention so that we can conserve water.

Every year we celebrate World Water Day on 22 March. This day is celebrated to spread awareness about the importance of water and run campaigns to conserve water on Earth. There are several ways to conserve water such as switching to showers, turning off taps when not in use, don’t pollute water bodies, storing rainwater, etc.

Also Read: Essay on Water Pollution

Essay on Water Conservation in 200 Words

Water is one of the Earth’s most precious resources. But the world is facing water scarcity. As per the SDA report 2022, around 2 billion people worldwide are lacking safe drinking water. This means they are more vulnerable to diseases and unhealthy life. 

Apart from the increasing population, climatic change is also hampering the quality of water. Floods and Droughts are more frequent due to the vulnerability of climate, thereby increasing the need to conserve water.

Water conservation is vital to meet the growing global demand for fresh water. Water consumption is very high for agriculture, industry, and households. By conserving water, we can ensure that there is a surplus amount of water to use and avoid conflicts over this limited resource.

Water conservation helps to maintain a balance in the ecosystem because every living thing on this planet is directly associated with the use of water. Reducing water consumption reduces the energy footprint associated with water supply.

The best ways of water conservation are rainwater harvesting , installing water plants, reusing water for gardening purposes, turning off taps when not in use, proper irrigation, installing automatic tap shut-off devices, not polluting water sources, and many more.

If we don’t want to witness the world die due to water scarcity then, it’s high time to conserve water and save the planet and future generations.

Also Read: Essay on Save Water

Water Conservation Essay 250 Words

Water conservation is a crucial step in protecting the environment. It is an important compound that supports life on Earth. The world has been facing water-related disasters due to scarcity of freshwater. 70% of the earth as well as the human body is composed of water, but there is a limited amount of freshwater to use. Owing to the ever-increasing population, climatic changes, global warming, and pollution, the need for the conservation of water is increasing. To do so, it is our fundamental duty to conserve water by planting more trees, managing water plants, storing rainwater, and making smart use of water. 

Water Scarcity

Water scarcity is a critical global issue that needs strict attention when the demand for freshwater exceeds the available supply of water. It can manifest in various ways, including a lack of access to clean drinking water, inadequate water for agriculture and industrial processes, and stressed or depleted natural water sources. 

Here are some factors that contribute to water scarcity:

• Climate change
• Growing population
• Global warming
• Inefficient water management
• Water pollution
• Increasing demand
• Poor irrigation techniques
• Wastage of water, and much more.

Ways to Conserve Water

Conserving water is crucial to help address water scarcity and ensure a sustainable water supply for both present and future generations. You can contribute individually by taking small measures to conserve water like turning off the tap. Likewise, here are some ways to conserve water:

• Drip irrigation technique
• Soil management
• Plantation of drought-tolerant crops
• Apply Mulching
• Recycle and reuse water
• Rainwater harvesting
• Desalination
• Spread awareness to conserve water
• Donate to the water cleaning campaign
• Implement proper water management techniques.

Also Read: Types of Water Pollution

Short Essay on Water Conservation

Find the sample of short essay on water conservation below:

Also Read: Essay on Save Environment: Samples in 100, 200, 300 Words

Water conservation is the individual or collective practice of efficient use of water. This helps in protecting the earth from the situation of water scarcity. We can individually contribute to water conservation by not wasting water, reducing the over-consumption of water, rainwater harvesting, etc. Water conservation is an important call because there is a limited amount of fresh water available on earth.

Here are 10 ways to save water. 1. Rainwater harvesting 2 Install water plants 3. Reuse water 4. Maintain proper water management plans 5. Fix the irrigation system 6. Use a bucket 7. Turn off the tap when not in use 8. Keep a regular check on pipe leakage 9. Do not pollute water bodies 10. Participate in water cleaning campaigns

Here are 5 points on the importance of water conservation: It helps the ecosystem; Water conservation is necessary for drought-prone areas; It helps reduce costs; Water conservation improves the quality of water; and Maintains the health of the aquatic ecosystem.

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English Compositions

Short Essay on Water [100, 200, 400 Words] With PDF

In this lesson today, I will discuss how exactly you can write short essays on the important topic ‘Water.’ There will be three sets of essays in this following session, each within different word limits. 

Short Essay on Water in 100 Words

Every living being on the earth needs some basic things for its survival. It includes food, water, shelter, and money as well for humans. Water is by far the principal need of living beings. About two-third part of the earth is covered with water.

Water is available in several forms on earth. Some amount is frozen in glaciers, while the larger amount of water is salty. Fresh water on earth is very little. We need water for every purpose. Drinking, cooking, bathing, washing are the basic needs, while water is also used by bigger industries to run their machines. Water is an important source of electricity. So, being the most valuable resource water must never be wasted.

Short Essay on Water in 200 Words

Water is the most significant resource among everything that humans and animals can receive. Water helps a living being to live for longer days, even when food is scarce. It is one of the most beautiful gifts of nature. Water has enormous benefits and is the life of the earth. Its medicinal properties cure several ailments in our bodies. Without it, we cannot imagine living a second on earth. The world will be a huge desert if the water on earth is destroyed.

Our earth is unique in its creation. About two-third part of it is covered with water, while the rest of it is land. If we take a deeper study, then a major part of the water is either frozen as glaciers or is present in the oceans as saltwater. The reserve of fresh water on earth is a limited amount. It can exhaust at any moment. Hence we must spend water wisely. We need water for drinking, bathing, washing clothes and utensils, cooking, cultivating, etc.

Big industries require lots of water to run their machines. Today due to the scarcity of coal, hydroelectricity is the new way of generating electrical power. This process requires huge amounts of water. In several ways, water is our saviour. It is the beauty of nature as a wonderful waterfall or a stream, and also the help to a thirsty person.

Short Essay on Water in 400 Words

Water is the basic strength behind all life forces on earth. It is the necessity of every life and is the biggest shelter for us to survive. If there is no water suddenly on earth, then it will only be a lifeless planet filled with dust and stone.

The green earth will become a long stretch of a desert without this component. Water forms about two-thirds of the earth, while only one-third is given for the land. Yet how much greater the amount of water on earth be, the availability of fresh water on earth is the minimum.

A large amount of water is left unused. It is either frozen as glaciers or is present as salty ocean water. This water cannot be applied for regular usage. So we must understand the wise utilization of water. It is a scanty but most important resource. So only its proper utilization can make it sufficient.

Water is the source of all activities in our lives. From the olden days, human beings have always tried to live near water bodies. Because those places are fertile for cultivation. A vast desert-like Egypt also survives because of the river Nile. The Ganges in India is not only a water body but one of the most sacred rivers in the world. The most important use of water is in agriculture.

Every plant needs it to grow. If crops do not receive adequate water, then they will be stunted. We use water for drinking, cooking, bathing, washing. A living body needs lots of water intake. Insufficient water intake can result in lots of ailments. Water is beneficial for this medical property. Besides these, all industries need water for producing electricity and running the turbines. Water is the potential of civilization. A civilization operates because of the availability of water

But at present, we are observing the pollution of water bodies. It is dangerous for all living beings to survive if all water sources are contaminated. Polluted water is a threat to the earth. Households, industries, insufficient cleanliness, lack of awareness, all are enough to increase pollution in several degrees. With increased consumption of water, it is being equally polluted. Thus many aquatic plants and animals, humans, other land animals are regularly dying after intaking the dirty water.

This is harming our ecosystem. So we must preserve freshwater. It is important and is available in little amount. Clean water can exhaust at any moment. It is our duty even to preserve the rainwater and use it. Every drop of water means life. A correct utility of it is the best way.

So, that was all about writing short essays on Water. In this session above, I have adopted a simplistic approach to writing all these essays for a better understanding of all kinds of students. You can let me know your queries by commenting down below. If you want to read more such lessons on various important topics regarding English composition, keep browsing our website. Thank you. 

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Essay On Plants

Plants are an incredibly important kingdom of organisms and one of the most important components of the earth. They help in the sustainability of life on this planet. Most plants are photosynthetic in nature. Photosynthesis is a process by which phototrophs convert light energy into chemical energy and this energy is later used to fuel cellular activities. Plants provide the foundation of many food webs and aid the survival of the animal kingdom. Here are a few sample essays on “Plants''.

100 Words Essay On Plants

A plant is a living thing which grows in the crust of the earth (soil), in water or on other plants; and usually has leaves, a long thin green central part called the stem, flowers, seeds and roots. A plant can be a young tree, vine, shrub, or herb. Plants belong to the kingdom “Plantae” of multicellular eukaryotic, mostly photosynthetic. Plants lack locomotive movement, and nervous or sensory systems and possess cellulose cell walls. Plants are classified by a system called taxonomy, which is based on their genetic and evolutionary relationship. Plant taxonomy is a branch of science that gets updated as new species are found almost daily.

200 Words Essay On Plants

Plants are multicellular organisms which can be distinguished by various features like they make their food. The study of plants falls under the subject of Botany. Botany has identified about 3,50,000 species of plants such as bryophytes, seed plants and fern allies. Green plants, also known as viridiplantae, prepare their own food in the presence of sunlight through a process called photosynthesis.

Source Of Food | Plants benefit us in a number of ways by providing seeds such as wheat, rice, corn etc that we eat in our daily life. Plants provide us with tasty fruits that give us minerals and vitamins. Apart from fruits and other food, plants also provide us with oxygen, shelter, fruits, food, timber, wood, fuel and medicine.

Preserve Ecosystem | Plants play an essential role in preserving the fauna and maintaining ecological balance. Without plants, human life would become miserable as we all are very much dependent on them. The absence of plants on earth will lead to desolation and deserts all around us.

Need To Protect | Thousands of plants are being cut down daily to make furniture and paper. All humans need to grow more trees and plants and protect the existing ones. Trees should be grown on bare cultivated land and forestry should cover a larger area.

500 Words Essay On Plants

Plants are incredible species which can use up abiotic components from the environment to make their own food and also give oxygen to the atmosphere, which is one of the basic factors for the sustainability of life on earth. The classification of plants is basically done on their evolutionary and genetic relationship.

Classification Of Plants

Plants can be classified on the following criteria:-

Vascular And Non-Vascular Plants

Plants can be classified as vascular or non-vascular:-

Vascular – the group of plants which possess the vascular systems to conduct food and water throughout the plant. They own true stems, leaves and roots.

Non-vascular – the plants which do not possess vascular systems. They have a stem and leaf-like structures and rhizoids instead of true structures.

Plants are also classified based on their life cycles:-

Annuals | These are the plants which live for only one season, that is they complete their entire life cycle in a single season. They are mostly herbaceous. Examples are wheat, rice, pulses, etc.

Biennials | These are the plants which complete their life cycle in two years. They are also herbaceous and examples are cabbage, carrot, beetroot and onions.

Perennials | These are plants having a long lifespan. They generally live for more than two years. They are either woody or herbaceous. Examples of perennial plants are lavender, dianthus and lilies.

Based on taxonomy, plants can be classified as below:-

Coniferophyta (Gymnosperms) | This group of plants is primarily evergreen and is found in the temperate zone. 700 species of gymnosperms are known to date. They are vascular, meaning that they do not flower. They do not bear fruits or flowers but produce seeds. Examples of gymnosperms are cycads, pines and cedars.

Anthophyta (Angiosperms) | This group of plants can grow into herbs, shrubs, bushes and big trees. 2,50,000 species of angiosperms are known to date. The trees we see around us are mostly under this category. Angiosperms are characterised by their seeds, fully enclosed in fruits. Examples are roses, mango trees, etc. They are further divided into -

Monocotyledonous – These plants are called monocot plants. These are flowering plants which have seeds that contain only one cotyledon. The leaves of these plants have a venation pattern, and it is a parallel vein. Examples are rice, sugarcane and corn. Over 50,000 species of monocot plants are known.

Dicotyledonous – These dicot plants are flowering plants, and they grow as herbs, shrubs, and trees. The seeds have two cotyledons. It has a net-like vein pattern, and the leaves radiate outwards from the main central vein. Examples of dicotyledonous plants are eucalyptus and figs.

Plant kingdom can be broken down into further divisions like:-

Thallophyta | This is the division which includes various kinds of microorganisms like fungi and algae. These algae can be further divided into green, brown and red algae.

Bryophyta | These plants are found in water and land, examples are mosses, liverworts and hornworts.

Pteridophyta | This group of plants do not have any flowers or seeds like ferns and club mosses. Ferns have true roots, stems and leaves, produced by spores. The life cycle of these plants depends on spores rather than seeds and preceded seed-forming reproductive processes.

Gymnosperm | This group have uncoated seeds that are exposed for reproduction. and the seeds are often born in cones that are not visible until maturation.

Angiosperm | These are also called flowering plants and their seeds are protected in an ovary. Fruits are born from the flower of the plant, which is formed from the seeds (ovules) in the ovary which is often enclosed in a flower, and in turn, contains seeds for reproduction.

My Fondness For Plants

I am a person who loves gardening. My love for plants is increasing day by day as I get to see these growing. These plants not only give us food but also add to the aesthetics of one's house. When I see those flowers or fruits on the plants, it makes me feel like I’ve forgotten all my worries. Thus I believe, plants have the ability to uplift one’s emotional strength too.

As a child, I went to nurseries with my mother and saw how well taken care of the plants were. It was such a fascinating thing for me that I gradually developed an interest towards plants. Also, being a passionate home cook I love using various kinds of herbs that add a different dimension to the food and also make it prettier.

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Essay on Plants

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In this essay, an attempt has been made to present briefly about plants. After reading this essay you will learn about: 1. Introduction to Plants 2. Do Plants Breathe? 3. Chemical Composition 4. Elements Essential for Healthy Growth 5. Different Organs 6. Uses 7. Characteristics 8. Factors Affecting Plants 9. Nomenclature 10. Groups 11. Water Absorption 12. Importance of Water 13. Ecological Classification and Others.

Essay Contents:

• Essay on the Photoperiodism in Plants

Essay # 1. Introduction to Plants:

Plants are the silent workers of our planet, they want to live and also help others (animals including human beings) to live. They have well-developed metabolic system, which includes both anabolism (synthesis) and catabolism (break­down). On the other hand, animals have only catabolic system.

Anabolic system, like photo­synthesis, is present in most of the plants and catabolic system, like respiration, is present in all plants. Photosynthesis is dependent on light, but the respiration occurs both day and night (throughout their life period). Photosynthesis requires CO 2 , water, chlorophyll and light. Plants can absorb CO 2 from the atmosphere and also utilize the CO 2 produced from its own respira­tion.

Water is being absorbed by plants from the soil. Chlorophyll absorbs light mainly from the sun (like an antenna of a T.V.). The resultant product is the carbohydrate (mainly glucose) and O 2 is released in the atmosphere as by-product. This O 2 is utilised by both plants and animals. The above fact indicates that the rate of O 2 production in plant is much more than that of respi­ration.

Thus, the produced O 2 becomes available to animals in sufficient amount. The product of photosynthesis – the carbohydrates is being utilised by the plants during respiration and the excess food is being stored in different organs. We snatch the food and other products from their storehouse. On the other hand, during respiration the O 2 is being used up and CO 2 released.

The CO 2 level in the atmosphere is being increased day by day, mainly due to three reasons:

i. Rapid destruction of forest by natural fire or artificial destruction of forests to get more agricultural land and also for urbanisation,

ii. Combustion on a large scale of wood and fossil fuels, such as coal, natural gas and mineral oil etc., and

iii. From respiration by the overgrowing human population (645 crores) of the world.

If the number of population of plant gradu­ally reduce (by natural hazards or artificial destruction by human beings), the amount of CO 2 will also gradually increase (CO 2 plays the most vital role in trapping the heat radiated from the earth) to cause global warming due to green­house effect.

The CO 2 contributes about 60% of the greenhouse gases. (Besides CO 2 , the princi­pal greenhouse gases are water vapour, methane, nitrous oxide, tropospheric ozone, chlorofluoro- carbons and halons).

Due to green-house effect, the temperature of the earth is gradually increa­sing which eventually will cause more melting of ice-caps and glaciers of the polar regions of the earth (Greenland, Antarctica), the floating ice on the water of the seas may also melt partially.

These will cause expansion of the volume of sea water, as a result the sea water level may rise. The rise of sea water level may cause the reduc­tion of our agricultural and living area due to flood.

So plants are very essential for the sustainability of animals, including human beings, to get O 2 for respiration, for reducing the amount of CO 2 from the atmosphere, for food, medicine, social functions etc. So, throughout history, men showed their keen interest to study the plant as a whole.

ADVERTISEMENTS: (adsbygoogle = window.adsbygoogle || []).push({}); Essay # 2. Do Plants Breathe?

Plants require oxygen for respiration and release carbon dioxide. For this gaseous ex­change, they unlike animals, have no specialised organs. It occurs by diffusion through stomata, lenticels and epiblema cells.

Reasons for Absence of Respiratory Organs in Plants:

i. Each part of plant takes care of its own gas exchange needs. There is little transport of gases from one part to another.

ii. Plants do not require much demand for gas exchange. All plant parts respire at rates far lower than animals.

iii. Leaves are well adapted to take care of their own needs of gases during photosyn­thesis. Moreover, leaves also utilize oxygen released during photosynthesis.

iv. In plants, cells are closely packed and located quite close to the surface of the plant. Thus the distance that gases must diffuse is not large.

v. In stems, the living cells are present beneath the bark and are in contact with air through lenticels.

vi. Epiblema cells of root are permeable to CO 2 and O 2 .

vii. Loose parenchyma cells in leaves, stem and roots provide interconnecting network of air spaces for quick gas exchange.

Thus most cells of a plant have at least one part of their surface in contact with air.

Essay # 3. Chemical Composition of the Plants :

Plant body is made of material units, cells. Each cell has proto­plasm usually surrounded by a rigid wall. Protoplasm undergoes metabolic changes and produces many ergastic substances. As plants cannot take solid food, they manufacture complex organic matters out of simple substances. We know that the whole animal kingdom, including human beings, has to depend on plants for the supply of food.

Chemically, protoplasm is a very complex matter having proteids, carbohydrates, fats, and other inorganic substances in composition. Proteids are made of carbon, hydrogen, oxygen, nitrogen, and in addition, often sulphur and phosphorus; carbohy­drates and fats are composed of carbon, hydrogen and oxygen. Cell wall is primarily made of insoluble carbohydrate, cellulose.

An idea about the chemical composition of the plant body can be had by the following method. A plant is dried at a high temperature. Naturally it will lose water. The percentage of water in plants is very high, often as much as 95%. The proportion of water can be determined by proper weighing. The dried plant gets charred forming a black mass of charcoal.

That is mainly carbon which forms almost half the dry weight of the plant. Now it is burnt. The combustible matters like proteins, carbohydrates and fats are converted into carbon dioxide, sulphur dioxide, ammonia, water vapour, and other gases and thus escape, which may be properly collected and composition noted.

The white in­combustible residue left behind is ash, which is nothing but the oxides of the metals constituting the plant body. The percentage of ash varies; but on the average, it forms nearly 5 per cent, of the total weight of the plant. On proper analysis ash is found to be composed of quite a large number of elements, many of them, of course, being present only in minute traces.

The following elements are, however, always present in ash: potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), sodium (Na), sulphur (S), phosphorus (P), chlorine (CI), and silicon (Si). Elements like manganese (Mn), boron (B), zinc (Zn), copper (Cu), and molybde­num (Mo) may be present in slight traces.

ADVERTISEMENTS: (adsbygoogle = window.adsbygoogle || []).push({}); Essay # 4. Elements Essential for Healthy Growth of a P lant:

It is found that thirteen elements are constantly present in the plant body, as revealed by ash analysis. The mere presence in the composition does not necessarily mean that they are all essential for the growth and nutrition of plants. What elements are essential and what are not, can be determined by water-culture experiment.

As plants absorb most of the elements from soil, a standard solution is prepared with those elements, and plants are grown there. By conducting a series of experiments (to be discussed presently) it has been found that ten elements are very important for the nutrition of plants and the remaining three, referred to as non-essential elements, are not directly concerned with nutrition.

It has been found that minute traces of the elements like boron, zinc, copper, manganese, and molybdenum are equally necessary for the normal development of the plants. Thus essential elements are put into two groups.

Essential elements:

i. Major elements are macro-elements—C, H, O, N, S, P, K, Mg, Ca, Fe.

ii. Trace elements or micro-elements—B, Zn, Cu, Mn, Mo.

That the above elements are essential for the healthy growth of a plant can be proved by water-culture experiment (Fig. 162). It is undoubtedly a laborious one. A few wide mouthed jars are taken, thoroughly washed and rinsed in nitric acid. Seeds are germi­nated on sterilised saw dust.

A few healthy seedlings of more or less same size are selected for experiment. Jars are labelled as 1, 2, 3, 4 and so on. The first jar 1 is filled with normal culture solution, i.e. a solution with all the elements essential for growth of plants. Culture solution should not be alkaline. Culture solutions of various compositions are used. Knop’s normal culture solution is a quite suitable one.

Knop’s normal culture solution :

Potassium nitrate, KNO 3 —1 – 0 g.

Potassium phosphate KH 2 PO 4 —1’O g.

Magnesium sulphate MgSO 4 —1 ‘0 g.

Calcium nitrate, Ca(NO 3 ) 2 —3’0 g.

Ferric chloride, FeCl 3 —a few drops.

Water—6 litres.

Jar No. 1 is filled with normal culture solution; a healthy seed­ling is selected and the roots after proper washing are inserted in the jar through the cork fitted at the mouth. A bent glass tube is put for aeration of roots and the jar is covered by black paper to cut off light.

Now a series of jars are similarly filled with plants but one element, in turn, is eliminated from the solution poured in every jar; thus jar 2 has no potassium salt, jar 3, no calcium salt and so on. Thus the experiment is set up.

After a few days it is observed that only the first one is having normal healthy growth and the rest are all weak, deficient, and stunted. Plant in jar 2 without potassium salt is weak and bears unhealthy leaves; in jar 3 without calcium salt the plant has poorly developed roots and spotted deformed leaves; leaves are yellow (chlorotic) in that without iron salts, and so on.

That shows be­yond doubt that the elements used in water culture solution and hydrogen, oxygen and carbon are absolutely necessary for the healthy growth of the plant. The essential elements are absorbed either as salts and compounds from the soil or as gas from the air by the two main absorbing organs, roots and leaves.

Recent re­searches have, however, shown that minute traces of manganese, boron, zinc, copper and molybdenum are also essential for normal growth.

Unlike the essential elements, they do not enter into the composition of plant body but they are absolutely essential as catalysts or growth regulators. Deficiency symptoms of these trace elements are not always observed for they are generally present in the soil or in the water culture where even the very pure analar reagents have traces of these elements.

The requirements of these trace elements are fantastically small, not more than 1-3 parts per 100 million parts. Carbon is absorbed from the air as carbon dioxide gas. Though the percentage of this gas in atmosphere is 0 – 03, that is the only source of carbon for the plants which really forms nearly half of the dry weight of the plant and is the primary constituent of proto­plasm, cell wall, food matters, etc.

Hydrogen and oxygen are taken mainly as water from the soil. Free oxygen is also absorbed from air during respiration. They enter into the composition of cell wall, reserve materials, and the protoplasm itself. Water is indispensable for protoplasmic activities and also for translocation of dissolved food materials.

Nitrogen forms an important element of protein and a consi­derable part of protoplasm. Though atmosphere has 78% of mole­cular nitrogen, it is not available to plants as such. It enters all visible plants and animals and comes out again without taking part in the life processes. Nitrogen mainly comes from soil as nitrates and ammonia salts.

The soil bacteria play important roles in converting nitrogenous matters into nitrates for ready absorption. Atmospheric nitrogen can be fixed by some free nitrogen-fixing bacteria and also by some bacteria which inhabit the roots of leguminous plants forming characteristic nodules.

The legume bacteria lead a life of mutual friendship (symbiosis) with the plants. The amount of nitrogen fixed by the bacteria is not very high—about 10% of the total nitrogen fixed in the soil.

Certain blue green algae can also fix nitrogen, which has considerable economic importance in increasing fertility of the rice fields, particularly in the tropics. During thunder storm free nitrogen becomes available to some extent. The nitrogen of the air combines with oxygen to form nitric oxide—N a -+ O 2 =2NO. This nitric oxide unites with O 4 of form nitrogen peroxide—2NO+O 2 =2NO 2 .

The nitrogen peroxide dissolves in falling rain water and forms nitrous acid and nitric acid—2NO 2 +H 2 O=HNO 2 +HNO 3 , and reach the soil, where they combine with metals like calcium and potassium to form nitrites and nitrates.

The nitrates are directly absorbed by the plants, whereas the nitrites are further oxidised to nitrates. Insectivorous plants get part of their nitrogen requirement from the bodies of the insects they capture.

Nitrogen occurs in the soil in organic form as complex proteins, and in inorganic form as nitrates and nitrites, and also ammonia and ammonium ions. The proteins of plant and animal bodies are broken down to simpler substances by the action of decomposers, the soil micro-organisms and fungi.

Ammonia is such a simple substance which readily dissolves in water. It reacts chemically with H-ions to form Ammonia ions NH 4 +. Only some plants can utilise nitrogen in this form for building up complex proteins. In case of most of the plants a group of micro-organism called nitrifying bacteria of the soil are responsible for converting the ammo­nium compounds into nitrates.

The process nitrification, as it is called, occurs in two stages—first, by the action of nitrite-bacteria ammonium compounds are oxidised into nitrites (NO 2 – ), and then nitrites are acted upon by the nitrate-bacteria to be finally oxidised into nitrates (NO 3 – ). Nitrates thus formed are readily absorbed by the plants and utilised.

Nitrifying bacteria work only under aerobic condi­tions, i.e. when oxygen is available. Under anaerobic condition another group of micro-organism, the denitrifying bacteria change the remaining nitrates into free nitrogen which gradually escapes to the atmosphere.

The whole picture, referred to as nitrogen cycle is represented by the following schematic diagram;

Sulphur is absorbed as sulphate from the soil. It is present in proteins and protoplasm.

Phosphorus is also obtained as phosphates from the soil. It is richly present in nucleo-proteins and has direct influence on cell-division and growth.

Potassium is absorbed as salts from the soil. It is important for the formation of healthy vegetative organs and maturation of fruits and seeds. Potassium is present abundantly in the meriste­matic region. It helps in the synthesis of reserve materials—carbo­hydrates, proteins, and fats.

Magnesium is also taken as salts. It is present in chlorophyll and has influence on the formation of proteins.

Calcium is essential for healthy growth. In absence of cium, plants get diseased. It is abundantly present in the middle lamella of the wall. Calcium neutralises organic acids like oxalic acid forming calcium oxalate. It is also absorbed as salts.

Iron does not actually enter into the composition of chlorophyll, but minute quantities are essential for the formation of chlorophyll. Plants become chlorotic in absence of iron. Perhaps iron acts as a catalyst for the formation of complex chlorophyll structure.

Sodium, chlorine, and silicon are present in the ash. But they are not essential for the normal growth of the plants.

Essay # 5. Different Organs of Plants:

It has a long cylindrical un-branched or branched axis or plant axis that bears a number of lateral appendages. Plant axis is differentiated into above ground shoot system and underground root system. Root system is usually brown and develops from radical part of embryo. Shoot system is at least partly greenish.

It grows from plumule part of embryo. Root system consists of root and its branches. Shoot system is made up of a stem, its branches, leaves, flowers, fruits and their contained seeds. The different structures borne on the plant axis are called organs. There are two types of plant organs, vegetative and reproductive.

Reproductive organs are meant for formation of new plants while vegetative organs take part. In nutrition, growth and maintenance of plant body. Vegetative organs are three in number— root, stem and leaves. Reproductive organs are also of three types— flowers, fruits and seeds.

Types of Plant Organs:

I. Vegetative Organs:

Some of the vegetative organs are:

It is the underground non green part of the plant that anchors the plant to the soil and takes part in absorption of water as well as minerals. Typically, there is a main or tap root, its branches or secondary roots, tertiary roots, etc. The finer root branches are called rootlets. The tip of a rootlet is covered by a root cap. Behind the tip are present a number of fine outgrowths called root hairs.

It is commonly the above ground erect part of the plant. It bears lateral branches. At intervals the stem and its branches possess swollen areas or nodes. Leaves are borne in the region of nodes. Part of the stem between two adjacent nodes is called inter­node.

The angle between the leaf and the upper or younger part of stem is called axil. It bears an axillary bud which later on develops into a branch or axillary branch. Growth of the stem or its branch is accomplished through a bud present at its tip. It is known as terminal or apical bud. The term shoot is applied to stem along with its leaves.

iii. Leaves:

They are green dissimilar lateral outgrowths which develop on the stem or its branch in the region of nodes. A leaf has three parts— leaf base, petiole and lamina. Lamina or leaf blade is specialized for photosynthesis. It is also the main seat of transpiration.

II. Reproductive Organs:

Some of the reproductive organs are:

It is a specialized and condensed shoot that takes part in sexual reproduction. A flower has a broad surface called thalamus or torus. The latter bears four types of structures— sepals (green), petals (coloured other than green), stamens (microsporophyll’s) and carpels (megasporophylls).

Sepals and petals are nonessential floral organs while stamens and carpels are essential floral organs. A stamen has a broad terminal anther that contains tiny structures named pollen grains or microspores. A carpel has receptive tip or stigma, a stalk-like style and a basal swollen part named ovary. The ovary contains one or more oval structures termed ovules.

It is the name of ripened ovary. Fruit has a wall or pericarp and one or more seeds.

It is a ripened ovule. Seed has an embryo, a food reserve and protective covering called seed coat. The embryo has an axis (embryo axis or tigellum) and one or two seed leaves called cotyledons. One end of embryo axis possesses plumule or future shoot.

The other end has radicle or future root. Radicle often bears a root cap at its tip. Plumule is protected by a few small leaves. The portion of the embryo axis lying between the cotyledons and the plumule is called epicotyls while the one between cotyledons and the radicle is termed as hypocotyl.

Essay # 6. Uses of Plants:

Humans showed interest in plant life for its various uses.

Our principal foods, like cereals, pulses, fruits and others are derived from the plants.

ii. Fibres:

Plant fibres like cotton, jute, flax and hemp are used in clothing and other purpo­ses.

Stem of different plants are used as wood in the preparation of furniture, boat, bridge etc.

iv. Other useful things:

Vegetable oil, resin, rubber, medicines, dyes etc., are directly or indirectly collected from the plants.

v. Fossil fuels:

Fossil fuels, such as coal, petroleum and natural gases are the pro­ducts of plants of past geological period.

vi. Soil erosion:

Trees and grasses that grow in different places help to retain water and thus prevent soil erosion.

vii. Shelter:

Plants in the forest provide good shelter and food for the birds and wild ani­mals.

viii. Supply of nitrogen:

Some plants, like algae and bacteria can fix atmospheric nitrogen and increase soil fertility.

ix. Aesthetic pleasure:

Plants give us aesthetic pleasure, which cannot be measured in terms of money.

x. Ecological balance:

In addition to the above importance, plants are with us as a friend to sustain our environment by absorbing excess CO 2 from the nature and releasing O 2 to the atmosphere and thereby they help us to survive in our immediate environment. Thus the human beings are now realising the importance of the plants.

(The Greenhouse Effect is the rise in tempe­rature that the earth experiences because of certain gases in the atmosphere such as water vapour, CO 2 , nitrous oxide, methane, tropospheric ozone, chlorofluorocarbons and halons. Without these gases, heat would escape back into space and Earth’s average temperature would be about -18°C. Thus, these gases are referred to as greenhouse gases.)

Essay # 7. Characteristics of Plants :

The important characteristics of the plants are:

i. Life cycle:

Each plant has a definite life cycle and within that cycle each plant carries out different activities like growth, reproduction etc. in a definite sequence from birth to death.

ii. Cell structure:

Plant body is made up of one or more structural unit, the cell. Protoplasm of each cell is enclosed in a membrane, called cell membrane. The cell membrane is further enclosed by a hard covering, the cell wall.

iii. Protoplasm (Protos – first; plasma – form):

It is the actual living matter of a cell, which performs all the vital activities.

iv. Metabolism:

Sum-total of biochemical changes that takes place in the protoplasm of a living cell is called metabolism. Metabolism includes both anabolism and catabolism. Anabolism is a process by which the simple food particles are produced and stored in the protoplasm, e.g., photosynthe­sis.

On the other hand, catabolism is the pro­cess by which the stored potential energy (food) in the protoplasm is converted into kinetic energy, e.g., respiration. In this pro­cess the stored food materials are utilised.

v. Nutrition:

Plants require nutrients for the synthesis of their protoplasm and also for their growth. Plants can synthesise their foods through photosynthesis.

vi. Respiration:

Respiration is a continuous pro­cess in plants, in which they usually take up O 2 from the atmosphere for oxidation of food materials (carbohydrate, protein etc.) and, as a result, release CO 2 and energy. This energy is required to perform all the vital activities of plants.

vii. Growth:

It is the permanent increase in form as well as volume of plant, usually accom­panied by increase in dry weight. The growth is the final product of successful metabolism, where the rate of anabolism is much higher than catabolism. In many plants, growth continues indefinitely.

viii. Reproduction:

All plants possess the capa­city to produce offspring of their own type. It is of three types – vegetative, asexual and sexual.

ix. Movement:

Most of the plants are not able to move from one place to other and generally they perform the movement of curvature. Only some lower plants (e.g., Chlamydo- monas, Volvox etc.) can move from one place to other.

x. Adaptability:

They have the power to adjust with the environment.

xi. Sensitivity:

The plants are very much sensi­tive to change in the environment.

xii. Excretion:

They can produce nitrogenous (Quinine, Nicotine, Atropine, Caffeine etc.) and non-nitrogenous (Resin, Gum, Latex, Tannin etc.) substances as by-products of metabolism, which are either stored or excreted from their body.

Essay # 8. Factors Affecting Plants:

Some of the factors that are affecting plants are described below:

i. Climatic Factors :

Important climatic factors affecting plants are temperature, light, humidity, precipitation and wind. All the factors are interdependent. Further, climate markedly affects soil and biotic factors. In a fast country like ours climate varies from tropical to temperate.

We have seen that all physiological processes go on most actively at optimum temperature which is widely variable with plants and climatic conditions. There are the cardinal points, minimum and maximum, below and above which activities are not possible, light is the ultimate source of radiant energy indispensable for photosynthesis. It has positive influence on transpiration, growth, development and movement.

Water vapour present in air is termed atmospheric humidity. It precipitates mainly in form of rain. A part of rain water percolates down the soil and becomes available to the plants. Rainfall has marked effect on vegetation.

In our country rainfall varies from about 7 – 5 cms or 3 inches a year in the arid regions of Rajputana to nearly 1200 cms in Cherrapunji in Meghalaya, the region of the highest rainfall in the world. In India rains are asso­ciated with monsoon winds.

Wind profoundly affects the rate of transpiration, dispersal of fruits and seeds and shape and branching of trees. Plants adjust themselves to stand against high wind pre­vailing in situations like sea-shore and deserts.

ii. Edaphic Factors:

Physical nature and chemical properties of soil, and particularly amount of water present in the soil available to the plants are important edaphic factors.

iii. Biotic Factors :

These include influence of living things on plants. Men, graz­ing animals, birds, earthworms, and even fungi and bacteria present in soil variously influenced the vegetation.

Essay # 9. Nomenclature of Plants :

Plants identified and described must be named. Though almost all the plants have common names but they do not serve our purpose. For proper co-ordination amongst workers names should be internationally acceptable. Linnaeus introduced ‘bi­nomial system’ of nomenclature which has been followed all over the world. Every name has two parts, the generic part and the specific part.

The generic part of the name is written in capital and the specific part in small initial letter. Both the names as a ride are indicated in italics and the name of the author in Roman script. Banyan is Ficus benghalensis, pipul is Ficus religiosa and fig is Ficus hispida. So all the three belong to the same genus Ficus but form different species.

The abbreviated name of the author or the person who first published the name of the plant with a suitable descrip­tion, is put after the specific name. Pea is Pisum sativum Linn. Here Linn indicates that Linnaeus was the author.

Essay # 10. Groups of Plants:

At present, about 400,000 different species of plants are recorded throughout the world in different habitat. So, it is very difficult to study the plants without following a definite system.

It is mentioned in Upanishads that Indians had studied the plants from medical point of view. But, the scientific attempt on the classification of plants began with the classical work of the Greek philosopher, Theophrastus (372-286 B.C.) in “Historia Plantarum”.

Later, in 16th century, many herbalists like Brunfels, Fuchs made some valuable contributions towards the study of Systematic Botany. After a long gap, in 18th cen­tury, remarkable contribution was made by a Swedish botanist, Carolus Linnaeus or Carl Linne (1707-1778).

His classification first appeared in Hortus Uplandicus (1732), with more detail in Genera Plantarum (1737), and later he comple­ted his work and presented it in Species Plantarum (1753). Thus, he is considered as the “Father of Modern Botany”.

Later on, many workers like de Candolle, Bentham and Hooker, Eichler, Engler and Prantl, Hutchinson, etc., and recently Takhtajan, Cronquist, Dahlgren and Thorne have proposed their classifications. The classification of Bentham and Hooker appeared in Genera Plantarum (1862-1883) – it is being followed in Indian Herbaria and also found to be easy to understand by the beginners.

Thus, the brief outline of classi­fication of Bentham and Hooker is mentioned:

The plant kingdom has been classified into two sub-kingdoms:

i. Cryptogamia, the non- flowering plants, and

ii. Phanerogamia, the flow­ering plants.

The cryptogamia has been further divided into three divisions :

A. Thallophyta,

B. Bryophyta, and

C. Pteridophyta.

A. Thallophyta:

Plant body is thallus-like i.e., not differentiated into root, stem and leaves. This group consists of most primitive and simple plants. The plants may consist of single cell (unicellular) or many cells (multi­cellular) and the sex organs are, in general, unicellular.

Based on the modes of life pro­cess, it is divided into four sub-divisions:

c. Bacteria, and

They are green in colour due to the presence of green pigment chloro­phyll and because of chlorophyll they are able to prepare their own food i.e., they are autophytes. The lower forms are unicellular, but the plants of higher forms are multicellular and become differentiated into organs resembling root, stem and leaves (Fig. 1.1).

They are devoid of green pig­ment, the chlorophyll and are not able to prepare their own food. They, therefore, live as saprophytes on dead and decay­ing vegetables or on organic materials or as parasites on living organism, i.e., they are heterophytes (Fig. 1.2).

They may be unicellular (Saccharomyces) or multi­cellular (Agaricus, Polyporus) and the largest known organism in this world is the fungus Armellaria bulbosa (mycelial body) reported from America, which covered an area of more than 12 hectares (30 acres).

Some fungi are destructive in nature, cause diseases of plants (brown spot of rice, late blight of potato caused famine in Bengal and Ireland, respectively). Some of them are very useful, as they yield valuable drugs (Penicillin from Penicillium notatum and P. chrysogenum) and some others are used as food, the mushrooms (Agaricus brunnescens, A. campestris, Pleurotus sajor-caju etc.)

These are microscopic, uni­cellular microorganisms with a sapro­phytic mode of nutrition (Fig. 1.3). They may be pathogenic and at times cause alarming situation in the plants and ani­mals including human beings. Some are useful to increase the soil fertility by adding nitrogen through fixation of atmospheric nitrogen.

(d) Lichens:

These are specialised organisms, composed of algae and fungi (Fig. 1.4). They live together in a close symbiotic association. The algal partner is capable of manufacturing food and, on the other hand, the fungus helps in absorption and retention of water. Though symbiotic, the tungal partner commonly dominates over algal part­ner. Lichens are used as food, fodder and in the manufacture of soap, dyes, perfumes etc.

B. Bryophyta:

The plant body of bryophytes is thailoid (Riccia, Marchantia etc.) or may be differentiated into stem and leaf-like organs (Funaria, Polytrichum etc.), but does not possess any true root (Fig. 1.5). They are usu­ally found to grow in moist and shady places and are of little economic importance. Starting from Algae up to Bryophytes, the dominating plant body is gametophyte i.e., haploid (n).

C. Pteridophyta:

It is the highest group of cryptogams. Starting from Pteridophyte onwards, the dominating plant body is sporophytic (2n). The plant body is com­pletely differentiated into root, stem and leaves (Fig. 1.6). They possess well- differentiated vascular system – for that they are called vascular cryptogams.

They generally grow in moist and shady places. Members, like Marsilea and some ferns (Ampelopteris prolifera etc.), are edible. Some fossil members contribute the world’s major fuel, the coal. The cone of Lycopodium is used in the production of an useful homeopathic medicine, named as Lycopodium.

The phanerogamia sub-kingdom is further divided into two divisions: Gymnospermia and Angiospermia.

The phanerogamia shows complete diffe­rentiation of plants into root, stem and leaves like Pteridophyta. In addition to the above characteristics, they also produce flowers and seeds. The dominating plant body of phanero­gams is sporophytic (2n).

I. Gymnospermia:

These are naked-seeded plants, i.e., the ovules are not enclosed in the ovary and thereby the seeds remain exposed or naked. Most of the plants are big trees (Fig. 1.7).

The group is economically important:

i. As a good source of timber.

ii. Some yield tar, charcoal, methyl alco­hol, tannin, etc.

iii. Some are used in the manufacture of paper, ink, etc.

iv. The valuable medicine ephedrine is prepared from Ephedra.

v. Like Pteridophytes, the fossil members contribute fossil fuels like coal, lignite, etc.

Common members are Cycas, Pinus, Cedrus, Ephedra, Ginkgo, etc.

II. Angiospermia:

These are closed-seeded plants, i.e., the seeds are enclosed in the ovary and thereby they remain enclosed within the fruits (Fig. 1.8). This group is further divided into two classes: Dicotyledons and Monocotyledons.

The class Dicotyledons comprises of the plants having two cotyledons or seed- leaves, e.g., Pea, Gram, Castor, Mango etc., and the plants of Monocotyledons having one cotyledon or seed-leaf, e.g., Rice, Wheat, Maize, Coconut etc. The plants under the Angiospermia show high eco­nomic value.

Essay # 11. Water Absorption in Plants:

i. Passive Water Absorption :

The force for this type of water absorption originates in the aerial parts of the plant due to loss of water in transpiration. This creates a tension or low water potential of several atmospheres in the xylem channels.

Creation of tension in the xylem channels of the plant is evident from:

(i) A negative pressure is commonly found in the xylem sap. It is because of it that water does not spill out if a cut is given to a shoot,

(ii) Water can be absorbed by a shoot even in the absence of the root system,

(iii) The rate of water absorption is approxi­mately equal to the rate of transpiration. Root hairs function as tiny osmotic systems.

Each root hair has a thin permeable cell wall, a semi-permeable cytoplasm and an osmotically active cell sap present in the central vacuole. Because of the latter a root hair cell has a water potential of -3 to -8 bars. Water potential of the soil water is -.1 to -.3 bars. As a result water of the soil passes into the root hair cell. However, water does not pass into its vacuole.

Instead it passes into apoplast and symplast of cortical, endodermal and pericycle cells and enter the xylem channels passively because of the very low water potential due to tension under which water is present in them, caused by transpiration in the aerial parts. A gradient of water potential exists between root hair cell, cortical cell, endodermal, pericycle and xylem channels so that flow of water is not interrupted.

ii. Active Water Absorption :

It is the absorption of water due to forces present in the root. Living cells in active metabolic condition are essential for this. Auxins are known to enhance water absorption (even from hypertonic solution) while respiratory inhibitors reduce the same. Therefore, energy (from respiration) is involved in active water absorption. Water absorption from soil and its inward movement may occur due to osmosis.

Passage of water from living cells to the xylem channels can occur by:

(a) Accumulation of sugars or salts in the tracheary elements of xylem due to either secretion by the nearby living cells or left there during decay of their protoplasts,

(b) Development of bioelectric potential favourable for movement of water into xylary channels,

(c) Active pumping of water by the surrounding living cells into tracheary elements.

Root pressure is a manifestation of active water absorption.

Essay # 12. Importance of Water in Plant Life :

Life originated in water. Lowest plants like the green algae live in water. Even to the higher plants, which through series of changes and adjustments have adapted themselves to terrestrial habits, water is of paramount importance.

Protoplasm, the physi­cal basis of life, remains saturated in a high -per­centage of water. In fact, functioning of the mysterious fluid proto­plasm depends on the large amount of water it contains. In the active and young vigorously growing cells water content is very high, approaching 95%.

In the hard woody portions the amount of water is nearly 50%. Dormancy of the seeds is due to low water content, varying from 10% to 15%. Protoplasm becomes less and less active if the normal amount of water is removed, until a point is reached when death ensues.

A certain amount of water in the vacuoles of the cells is neces­sary to maintain the normal condition of the turgor, what is essen­tial for the growth of the cells and also for the erectness of the plant. Water is essential for continual translocation from one part of the plant to another part. As far as it is known, all foods and dis­solved materials translocated in a plant move from cell to cell in watery solution.

Many of the various organic compounds are formed by the combination of water with certain materials that enter the plant from the soil and the air. A supply of water in the soil is also needed to replace the water lost by transpiration.

The process of absorption of inorganic salts by the root-hairs is very complex and little understood. Probably salts come in by diffusion through the plasma membrane independently of the movement of water.

Essay # 13. Ecological Classification of Plants:

As water is of the greatest importance to the plants, it is custo­mary to classify the plants into the following ecological groups on the basis of their water relation.

i. Hydrophytes or aquatic plants.

ii. Mesophytes, the common land plants, flourishing best in moderate water-supply.

iii. Xerophytes, plants of very dry regions like deserts.

iv. Halophytes, plants growing in sea-shore or saline marshes where absorption of water becomes difficult.

i. Hydrophytes :

These are plants which grow in situations with high percentage of water. They may be free-floating, submerged or amphibious.

Roots and analogous organs are very poorly developed as the plants can absorb water by entire surface. Stems are usually soft and spongy. Leaves are generally dissected, ribbon-like in sub­merged plants with very scanty cuticularisation. Stomata and palisade cells are lacking. Conducting and mechanical tissues are very poorly developed.

Air-spaces are abundant for giving buoy­ancy to the plants. Many aquatic plants often show heterophylly. Vegetative multiplication far exceeds sexual reproduction. Fruits and seeds are often provided with air chambers for facilitating dispersal by water.

Amphibious plants have poorly developed root system and ample air-spaces like typical hydrophytes; but they more or less resemble the mesophytes in characters of leaves and arrangement of conducting tissues. Common plants—Vallisneria (B. Pata shaola) Hydrilla, Utricularia (B. Jhanji), water-hyacinth, Pistia (B. Barapana lotus, lily, water-plantain, arrowhead.

ii. Mesophytes :

These are the common land plants growing in moderate water- supply. So far as structural peculiarities are concerned, they are intermediate between hydrophytes and xerophytes. Leaves are usually broad and thin and possess well-developed stomata. Pro­duction of root-hairs is a distinctive character.

iii. Xerophytes :

These are plants growing in very dry situations like deserts. They have adaptations to stand against extreme heat, dry air, intense light and high wind.

Root system is very strongly developed, both in length and volume. Aerial portions are stunted in growth. Transpiring sur­faces are very much reduced for minimising the loss of water. Leaves are often modified into spines and scales; they may be thin, rolled or folded.

Strong development of cuticle with extra-coating of wax, resinous matters, sunken stomata, formation of dense hairs, etc., are distinctive characters. Succulence for storage of water is very common. Common plants—Cacti, Opuntia (B. Fanimanasha), spurges, Ravenala (traveller’s tree, B. Pantha padab).

iv. Halophytes :

These are plants growing in saline marshes or on sea-shore where absorption of water becomes difficult due to the preponder­ance of salt. This type of soil is called physiologically dry.

Plants of saline marshes form a special type of vegetation of low forest, called mangrove, as found in Sundarbans. The plants produce stilt roots for extra support and special aerating roots or pneumatophores for absorbing oxygen from air.

Succulence is common in some plants. They usually show cymose type of branch­ing. A special mode of germination, called vivipary, is exhibited by the mangrove plants (Fig. 37). Common plants—Rhizophora, Heritiera (B. Sundri), Ceriops (B. Goran).

Essay # 14. Reproduction in Plants:

i. Vegetative Reproduction :

It is the simplest method, where parts may get detached from the parent plant and lead independent existence. In lower unicel­lular plants like yeast, outgrowths in form of buds come out which, in course of time, are separated from the mother cell. In filament­ous algae like Spirogyra the filament breaks up into one- or more- celled fragments, each of which may multiply and carry on inde­pendently.

Bryophytes like mosses and liverworts produce special bodies, called gemmae, and multiply through them. Ferns repro­duce vegetatively by rhizomatous stems. In higher plants vegeta­tive multiplication occurs through modified roots, modified stems like runners, rhizomes, etc., bulbils and adventitious buds.

Artifici­ally multiplication is secured by cuttings, layerings, buddings and graftings. These are common devices employed by the florists.

ii. Asexual Reproduction :

Here special minute, usually unicellular bodies, called spores, are formed which directly can produce new individuals. Spores may be naked or walled. Naked motile ciliated spores of algae are called zoospores. The spores of bryophytes, pteridophytes and higher plants are non-motile and have cell wall. The spore- containing sac is called sporangium.

iii. Sexual Reproduction :

This method essentially involves the fusion of two usually naked sexual or reproductive units called gametes. Individually gametes are of no use for reproduction, but by fusion they give rises to the zygote, which alone can produce a new plant. When the two gametes are morphologically similar, they are called isogametes.

Product of fusion of two isogametes is zygospore and the process is known as conjugation. Dissimilar gametes are called heterogametes. Obviously one of them is male and the other is female. Here zygote is called oospore and the process is fertilisa­tion.

Of the two heterogametes, the male, called antherozoid or spermatozoid, is, as a rule, much smaller than the female gamete and is motile and active. The female gamete is much larger, always stationary or sessile and passive. It is called egg, ovum or oosphere. The male gamete-containing sac is known as antheridium and the female gamete-containing one is oogonium or archegonium.

Parthenogenesis :

Though sexual reproduction essentially demands union of two gametes, in some lower plants one of the gametes (usually the female one) behaves like a zygote without uniting with the corres­ponding one. This process is called parthenogenesis, and the spore concerned is known as azygospore or parthenospore.

Apogamy and Apospory:

Normally the plants having sexual method of reproduction show an alter­nation of two generations-—gametophytes with haploid chromosomes, and sporophytes with diploid chromosomes. But there are cases in which one generation may be wholly or partly eliminated. If the eliminated part be gametophyte, the phenomenon is called apogamy; and if that is sporophyte, the phenomenon is known as apospory.

In many ferns buds may vegetatively develop on the prothallus which grow into sporophytic plants. Thus formation of sporophyte has taken place without the act of fertilisation, which is not certainly normal. In some seed- plants certain cells of the nucellus, which belongs to the sporophyte, may develop into embryos, thus completely eliminating the whole gametophytic generation. These are cases of apogamy.

Apospory is quite common in some ferns in which prothallus, the gameto­phyte, may develop from the sporangia, and even from the leaf. The prothallus so formed bears sex-organs like a normal one, though it has not developed from a spore. There are ferns and seed-plants which exhibit both apogamy and apospory.

Essay # 15. Transpiration in Plants:

Plants usually absorb water much in excess of their need through the innumerable root-hairs. Some amount of water is uti­lised for metabolic activities and the surplus goes out as water vapour. This process of getting rid of excess of water in the form of water vapour, is known as transpiration.

It may take place through the exposed aerial parts of the plants. But as structure and position of leaves are very much conducive to the process, they are the main transpiring organs of plants. It should be noted that transpiration is not simple evaporation, but a physiological process where the outgo of water is regulated by protoplasm. A twig detached from a plant would evaporate much more water than one attached to it.

Maximum transpiration takes place through the stomata present on the leaves. This is called stomatal transpiration. In day time the two guard cells manufacture sugar and thus the sap is concentrated. By osmosis they absorb water from the adjoining cells and become turgid, when they stand away from each other making the stomatal aperture wide open.

The spongy cells evapo­rate water into the intercellular spaces which accumulates at the sub-stomatal chamber and ultimately diffuses through the stomatal opening, provided, of course, the outside air is dry. At night the turgor pressure of the guard cells decreases and they become flaccid, naturally closing the aperture.

The epidermal cells have cuticle on the outer walls which is almost impervious to water. In plants of moist and shady places cuticle is very thin, and feeble transpira­tion becomes possible through it.

This is cuticular transpira­tion. It is about 10% of the entire transpira­tion through the leaf, the remainder being stomatal transpira­tion. In the still air, however, the rates of cuticular transpiration in many places have been found to be as high as 30% of the total transpiration through leaves. Trans­piration may also take place through the lenticels often referred to as lenticular transpi­ration.

The amount of water lost by transpi­ration is surprisingly. For example, a maize plant during a growing season may lose by transpiration as much as 246 litres or 54 gallons of water. Due to transpiration from the leaf surface, a pull or suction force is produced, as a result of which water is drawn upwards. This is termed as transpiration current.

Essay # 16. Translocation in Plants:

Plants lack both interstitial fluid as well as a regular circulation system. Even then they have to move (transport) various types of substances (gases, minerals, water, hormones, photosynthetic and organic solutes) not only to short distance (from one cell to another or from one tissue to another) but also to very long distances such as water from roots to tops of plants or photosynthetic from leaves to tips of roots.

Substances move over short distances through diffusion and active transport supplemented by cytoplasmic streaming. Long distance transport occurs through vascular systems, xylem and phloem.

This transport of substances over longer distances through the vascular tissue, i.e., xylem and phloem, is called translocation. It occurs through mass flow. The direction of translocation is essen­tially unidirectional in case of water (from root to stem, leaves, flowers and fruits). It is multidirectional in case of minerals and organic solutes. Organic compounds are synthesised in leaves.

They are exported to all other parts including every living cell, growing points, fruits and storage organs. Storage organs re-export the organic nutrients when new growth is to take place.

Certain parts re-export the products of their own biosynthetic activities. Mineral nutrients are primarily picked up by roots. They are passed out upwardly to leaves, stem and growing regions. Leaves re-export many of these minerals in organic form.

Senes­cent organs and leaves pass out most of their nutrients, especially the mineral ones, before falling down from the plant. Plant hormones and other chemical stimuli are transported in very small amounts. Some of them are transported in polarised or unidirectional manner while others diffuse to all parts.

Therefore, a complex traffic of materials is going on in flowering plants, some moving to different directions, some passing out in polarised manner, with most organs receiving some substances and giving out some others.

Essay # 17. Study of Mineral Nutrient in Plants :

Mineral requirements of plants is determined by culture experiment first developed by German botanist Julius von Sachs (1860). The technique is believed to have been initiated by Home (around 1750) and improved by Knop (1865).

Culture experiments are hydroponic experiments in which plants are grown from seeds to maturity in a defined nutrient solution in complete absence of soil. The early nutrient solutions were based on mostly macronutri­ents as micronutrients usually accompanied them as contaminants.

As the chemically pure salts became available, the importance of micronutrients became clear. The first complete prescription of all known mineral salts required for preparing culture solution was given by Amon and Hoagland (1940).

Iron is provided along with a chelating agent, Na-EDTA. Water used in preparing culture solution is twice distilled in glass containers. Salts are chemically pure. In culture experiments, a solution containing the various mineral elements is prepared.

A solution having all the essential elements in proper proportion is called normal or balanced nutrient solution. The element of which deficiency symptoms are to be studied is made deficient in the solution (Table 12.1).

Seedlings are reared either directly in such solutions (solution or water culture) or in earthen pots having sterilized sand (sand cul­ture). For studying the effect of microelements, cotyledons or other organs containing reserve food are removed because they are rich source of microelements.

In a typical solution culture technique, nutrient solution is placed in superior glass jars or polythene bottles covered with black paper (to prevent growth of algae and reaction of roots to sun­light).

The jars contain split covers or corks with holes for suspending seedling, a funnel for adding solution and a bent tube for aeration (Fig. 12.1). Regular aeration is required for proper growth and activities of roots. pH of solution is checked from time to time and correction made.

Culture experiments are use­ful in knowing:

i. Essentiality of mineral nutrients.

ii. Role of an essential element in body structure and protoplasmic constituents of the plants.

iii. Role of an essential element in the physi­ology of plants.

iv. Deficiency symptoms.

v. Toxicity due to excess of an element.

vi. Interaction of different elements.

vii. Role of a nonessential but functional element.

Essay # 19. Photosynthesis in Plants:

Photosynthesis (Gk. phos or photos— light, synthesis— putting together) is an enzyme regulated anabolic process of manufacture of organic compounds inside the chlorophyll containing cells from carbon dioxide and water with the help of sunlight as a source of energy.

A simple equation of photosynthesis is as follows:

However, the function of water is to provide hydrogen for the synthesis of organic compounds. All the liberated oxygen comes from it.

Therefore, the equation is modified as:

Importance of Photorespiration in Plants:

(i) Photorespiration does not produce energy or reducing power. Rather, it consumes energy. Further, it undoes the work of photosynthesis. There is 25% loss of fixed CO 2 . Therefore, photorespiration is a highly wasteful process. This happens only in case of C 3 plants.

C 4 plants have overcome the problem of photorespiration by evolving O 2 or performing or evolving light reaction in mesophyll cells and Rubisco mediated CO 2 – fixation by Calvin Cycle in the interior of leaves (bundle sheath cells) where both temperature and oxygen are lower. They have further ensured high CO 2 supply to cells performing Calvin cycle,

(ii) It helps in dissipation of energy where stomata get closed during daytime because of water stress,

(iii) Photorespiration protects the plant from photoxidative damage by dissipating excess of excitation energy.

Essay # 22. Plant Growth Regulators:

Plant growth regulators are small, simple molecules of diverse chemical composition, which in low concentration regulate growth, differentiation and development by promoting or inhibiting the same. One type of plant growth regulators are plant hormones or phytohormones.

Technically a plant hormone is a chemical substance other than nutrient pro­duced naturally in plants, which may be trans-located to another region, for regulating one or more physiological reactions when present in low concentration. Five types of phytohor­mones are known.

They are in-dole compounds (e.g., Indole acetic acid or IAA), adenine derivatives (e.g., furfuryl, amino purine, kinetin, cytokinins), derivatives of carotenoids and fatty acids (abscisic acid, ABA), terpenes (gibberellins, e.g., GA 3 or gibberellic acid) and gases (ethylene, C 2 H 4 ). Other related growth regulators are salicylic acid, jasmonic acid and brassinosteroids. Some vitamins also regulate plant growth.

PGRs are broadly divided into two groups, plant growth promoters and plant growth inhibitors. Plant growth pro-motors perform growth promoting activities like cell division, cell enlargement, pattern formation, tropic growth, flowering, fruiting and seed formation. They are three in number viz., auxins, gibberellins and cytokinins.

Plant growth inhibitors normally induce dormancy and abscission. They have, however, an important function in inducing plant responses to wounding, biotic and abiotic stresses. Abscisic acid is known plant growth inhibitor. Ethylene is largely plant growth inhibitor but is also involved in some growth promotion activities.

i. PGRs are involved in a variety of growth, differentiation and developmental re­sponses.

ii. The response to a PGR may differ from one plant organ to another. Auxin promotes growth of apical bud but inhibits growth of axillary buds. The concentration of auxin which promotes stem growth is inhibitory to root growth.

iii. Similar responses may be shown by different PGRs. Auxins and gibberellins promote cell growth while the three growth pro-motors (auxins, gibberellins, cytokinins) are involved in cell division.

iv. Plant growth regulators are effective at very low concentration, usually in the range of 10-6.

v. The site of production and site of action (target cells) of plant growth regulators may be different (as in case of animal hormones) or the same (unlike animal hormones).

vi. There is no specialised tissue or gland for producing a plant growth regulator. Instead it can be synthesized at many places by different tissues within the plant body.

Essay # 23. Photoperiodism in Plants:

The effect of photoperiods or daily duration of light hours (and dark periods) on the growth and development of plants, especially flowering, is called photoperiodism.

Photoperiodism was first studied by Garner and Allard (1920). They observed that Maryland Mammoth’ variety of Tobacco could be made to flower in summer by reducing the light hours with artificial darkening. It could be made to remain vegetative in winter by providing extra light.

On the basis of photoperiodic response to flowering, plants have been divided into the following categories:

(i) Short Day Plants (SDP, Fig. 15.28):

They flower when the photoperiod or day length is below a critical period. Most of winter flowering plants belong to this category, e.g., Xanthium (Cocklebur), Chrysanthemum, Cosmos bipinnatus, Aster, Dahlia, Rice, Sugarcane, Strawberry, Potato, To­bacco, Soya Bean varieties.

(ii) Long Day Plants (LDP, Fig. 15.28):

These plants flower when they re­ceive long photoperiods or light hours which are above a critical length, e.g., Henbane (Hyoscyamus niger), Wheat, Oat, Sugar Beet, Spinach (Spinacea oleracea), Radish, Bar­ley, Larkspur, Lettuce.

(iii) Short-Long Day Plants (S-LDP):

The plants require short photoperiods for floral initiation and long photoperiods for blossoming. They usually come to flower between spring and summer, e.g., Cam­panula medium, Petkus variety of Rye.

(iv) Long Short Day Plants (L-SDP):

The plants require long photoperiods for floral initiation and short photoperiods for blossoming. The plants flower between summer and autumn, e.g., Bryophyllum, Cestrum.

(v) Intermediate Day Plants (IDP):

The plants flower within a definite range of light hours. Flowering does not take place above and below this range, e.g., Wild Kidney Bean.

(vi) Day Neutral or Indeterminate Plants (DNP):

The plants can blossom throughout the year, e.g., Tomato, Pepper, Cucumber, Pea varieties, Sunflower, Maize, Cotton, etc.

Dark Periods (Skotoperiods):

Short day plants are also called long night plants because they require a continuous critical dark period, which must be exceeded, If the plant is exposed to even a flash of light (red, usually 660 nm) before achieving a critical dark period, flowering is prevented.

It is called light break reaction. Red light effect can, however, be prevented by immediately providing far- red light. Red, far-red exposures given in succession show that plant response is determined by the last exposure. It is, therefore, clear that photoperiodic response is mediated by phytochrome which shows reversible change in red (660 nm) and far-red (730 nm) wave­length.

In long day plants, the period of darkness should be shorter than a critical dark period. Light exposure during dark does not inhibit flowering in long day plants. Rather it promotes flowering. They also come to flower in alternate short light and still shorter dark periods. Long day plants can flower even when exposed to continuous light. Hence long day plants are also called short night plants.

Importance of Photoperiodism in Plants:

(i) Photoperiodism determines the season in which a particular plant shall come to flower. For example, short day plants develop flowers in autumn-spring period (e.g., Dahlia, Xanthium) while long day plants produce flowers in summer (e.g., Amaranthus). Day neutral plants can be made to flower throughout the year since their flowering is dependent more on temperature and vegetative growth (e.g., Tomato).

(ii) Knowledge of photoperiodic effect is useful in keeping some plants in vegetative growth (many vegetables) to obtain higher yield of tubers, rhizomes, etc. or keep the plant in reproductive stage to yield more flowers and fruits.

(iii) A plant can be made to flower throughout the year under green house conditions if a favourable photoperiod is being provided to it. This has been used by commercial growers to meet the demands of market for prized vegetables and flowers.

(iv) The phenomenon has helped the plant breeders in effecting cross-breeding in plants which normally develop flowers in different seasons.

(v) It has further been found that photoperiodic response of plants is under the control of genes. Manipulation of genes can enable a plant to flower in different seasons. This has actually been achieved by National Botanical Research Institute, Luck-now. The institute has developed varieties of Chrysanthemum which flower in different months of the year.

(vi) A proper knowledge of photoperiodism in relation to flowering is also highly useful in laying out gardens, orchards and planning crop pattern of the area.

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• Published: 28 April 2021

The relationship between plant growth and water consumption: a history from the classical four elements to modern stable isotopes

• Oliver Brendel   ORCID: orcid.org/0000-0003-3252-0273 1  

Annals of Forest Science volume  78 , Article number:  47 ( 2021 ) Cite this article

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A Correction to this article was published on 17 June 2021

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Key message

The history of the relationship between plant growth and water consumption is retraced by following the progression of scientific thought through the centuries: from a purely philosophical question, to conceptual and methodological developments, towards a research interest in plant functioning and the interaction with the environment.

The relationship between plant growth and water consumption has for a long time occupied the minds of philosophers and natural scientists. The ratio between biomass accumulation and water consumption is known as water use efficiency and is widely relevant today in fields as diverse as plant improvement, forest ecology and climate change. Defined at scales varying from single leaf physiology to whole plants, it shows how botanical investigations changed through time, generally in tandem with developing disciplines and improving methods. The history started as a purely philosophical question by Greek philosophers of how plants grow, progressed through thought and actual experiments, towards an interest in the functioning of plants and the relationship to the environment.

This article retraces this history by following the progression of scientific questions posed through the centuries, and presents not only the main methodological and conceptual developments on biomass growth and transpiration but also the development of the carbon isotopic method of estimation. The history of research on photosynthesis is only touched briefly, but the development of research on transpiration and stomatal conductance is presented with more detail.

Research on water use efficiency, following a path from the whole plant to leaf-level functioning, was strongly involved in the historical development of the discipline of plant ecophysiology and is still a very active research field across nearly all levels of botanical research.

1 Introduction

The ratio of biomass accumulation per unit water consumption is known today as water use efficiency (WUE) and is widely relevant to agriculture (e.g. Blum 2009 ; Tallec et al. 2013 ; Vadez et al. 2014 ), to forest ecology (e.g. Linares and Camarero 2012 ; Lévesque et al. 2014 ) and in the context of global climate change (Cernusak et al. 2019 ). This ratio can be defined at various levels, from the physiological functioning of a leaf to the whole plant and at the ecosystem level. This historical review starts at the whole plant level, where WUE can be simply measured by quantifying the amount of water given to a plant and the plant’s increase in biomass during the experiment. The ratio of biomass produced divided by the cumulative water lost during growth is termed whole plant transpiration efficiency (TE= biomass produced/water lost). Historically, the ratio has also been calculated in its inverted form (water lost/biomass produced) and various terms have been used to denote these ratios (see Box 1). As knowledge, concepts and technology advanced, it became desirable to measure TE also at the leaf level, where it is defined either as the ratio of net CO 2 assimilation rate to transpiration (or to the stomatal conductance for water vapour). Therefore, some history of the two leaf-level components of WUE is included here. Numerous articles have been published on the history of the development of research on photosynthesis, and other than the reviews cited in this article, the publications by Govindjee are notable, especially Govindjee and Krogmann ( 2004 ), as they include a long list of other writings on the history of photosynthesis. On the other hand, little has been written about the history of research on transpiration and stomatal conductance. Notable is Brown ( 2013 ), who wrote specifically on the cohesion-tension theory of the rise of sap in trees, including many writings from the late nineteenth century. Consequently, here, photosynthesis research is only broached briefly, whereas transpiration research is more detailed.

As the development of the research on WUE spans a very long period, starting with Greek philosophers, publications are in several languages. Classical writings were in Greek or in Latin, and for these translations are available. However, from the mid-seventeenth century onwards, national languages were more and more used, which can be seen in the number of French- and German-language publications. This review is also a tribute to these nowadays less known seventeenth, eighteenth and nineteenth century French and German natural philosophers and their contribution to the development of the science of plant ecophysiology. Also, towards the beginning of the twentieth century, publications became too numerous to allow a comprehensive review; thus, the author focussed on the use of the carbon stable isotopes methodology and on tree ecology.

Box 1 Short history of names for whole plant transpiration efficiency (TE)

2 What is plant matter made of?

Various Greek philosophers were interested in how substances can change from one thing into another. Thales (624–c. 546 BC) thought that all things come from water, whereas Anaximenes argued that “pneuma” (air) should be the basis of all things (Egerton 2001a ). These assertions were the basis of more than 2000 years of philosophical dispute.

In “De Causis Plantarum”, Theophrastos (371–287 BC) assumed that plants draw nutrition, which consisted of varying amounts of the four elementary humours, from the earth through their roots (Morton 1981 ). Some centuries later, in a Christian work translated in 400 AD from Greek into Latin and known as “Pseudo-Clement’s Recognitions”, an apparent thought experiment was described to “prove that nothing is supplied to seeds from the substance of the earth, but that they are entirely derived from the element of water and the spirit (spiritus) that is in it” (Egerton 2004c ). The author of this thought experiment suggested putting earth into big barrels, growing herbaceous plants in it for several years, then harvesting them and weighing them. His hypothesis was that the weight of the earth would not have changed, and the author used this as an argument that the vegetation biomass could have come only from water. This thought experiment revealed a progress in scientific thinking because the question was posed more precisely than before. It stood out at a time when botany mainly consisted of naming plants and “theoretical botany effectually went out of existence” (Morton 1981 ).

It appears that the question of how plant matter is produced was not pursued in Roman or Arabic writings, which were more concerned with agricultural (the former) and medical (the latter) aspects of plant sciences (Egerton 2001b , 2002 ). Not until the High Middle Ages was a renewed interest shown in plant growth. Adelard of Bath, a twelfth century English natural philosopher, devoted the first four chapters of “Questiones Naturales” (c. 1130–1140; Morton 1981 ) to the question of what plant matter is made of. He argued, within the concepts of the four elements theory, “by just as much as water differs from earth, by so much does it afford less nourishment to roots, I mean than earth does”, clearly being in favour of earth as the source for plant nourishment. His arguments were only theoretical and speculative.

A major step occurred in botanical sciences between the fifteenth and sixteenth centuries; scholars began making experiments to test antique and medieval hypotheses against observations in nature (Egerton 2003 ). In the mid-fifteenth century, and probably related to the translation and printing of the botanical books by Theophrastus (Morton 1981 ), the thought experiment from “Recognitions...” was taken up by Nicholas of Cusa in the fourth part of his “Idiota de mente”, “De staticis experiments”. At a time when the naming of plants for pharmacology was the major interest of savants, he proposed experimental investigations. Nicholas of Cusa described the same thought experiment as did Pseudo-Clement’s Recognitions ; he concluded similarly that “the collected herbs have weight mainly from water” (1450; translation into English by Hopkins 1996 ). Cusa additionally suggested that the plants should be burned at the end of the experiment and the ash weight be taken into account. It is not clear whether the thought experiment was ever physically done.

In the sixteenth century, botanical science began to separate from medical sciences, with the establishment of lectureships in universities (e.g. Padua in 1533) and the establishment of botanical gardens (Egerton 2003 ). The bases existed for advancing science in the seventeenth century of Enlightenment. Francis Bacon, an influential philosopher of his time, conducted a series of plant growth experiments which are reported in his “de Augmentis Scientiarum” (1623; Spedding et al. 1900 ). Bacon discovered that some plants sprouted more quickly in water than in soil (Egerton 2004b ). He concluded that “for nourishment the water is almost all in all, and that the earth doth but keep the plant upright, and save it from over-heat and over-cold” (Hershey 2003 ), thus still upholding the theory proposed by Thales and Nicholas of Cusa. In “The History of the Propagation and Improvement of Vegetable”, Robert Sharrock ( 1660 ) reported that some plants both rooted and grew entirely in water. Although he noted different amounts of transpiration over time, he did not discuss this in relation to plant growth.

In 1662, Johannes Baptista van Helmont published his now-famous willow experiments (van Helmont 1662 ). This may be the first report of an experiment that was based on the thought experiment of Nicholas of Cusa (Hershey 2003 ) with the minor differences of beginning with dried soil and not using herbaceous plants, but rather a willow tree. After weighing the soil, he irrigated it with rain water and planted the weighed stem of a willow tree. The experiment ran for 5 years. At the end, the tree was weighed again, as was the dried soil. He found the soil weighed about 2 ounces less than at the beginning of the experiment, whereas 164 pounds of wood, bark and roots was produced. He concluded that the organic matter could only have come out of the water. Helmont was unaware of the existence of carbon dioxide, but he did know of “gas sylvestre”. He also knew that burning oak charcoal would produce nearly the same amount of gas sylvestre and ash. However, he did not connect this information with the plant growth he had observed (Hershey 2003 ). Robert Boyle published similar experiments in “The sceptical Chymist” (Boyle 1661 ). Boyle claimed that he had done his experiments before he knew of Helmont’s (Egerton 2004c ), although he discussed Helmont’s results and arguments in detail in his book. Boyle doubted the direct transformation of water into plant matter. He admitted, however, that it might be possible that other substances contained in the water could generate new matter (Boyle 1661 ). In the 1660’s, Edme Mariotte also criticised van Helmont’s theory that water alone constituted the only element to produce plant matter. He thought similarly to Boyle that elements in the water could contribute to the plant matter. He also showed that nitrogen compounds were important for plant growth (Bugler 1950 ).

John Woodward, in his “Some Thoughts and Experiments Concerning Vegetation” (Woodward 1699 ), took up again the question of what comprised the source of plant growth. Woodward criticised Helmont’s and Boyle’s experiments, mainly on the precision of weighing the dry soil before and after the experiment, but also the contamination of the irrigation water by terrestrial vegetable or mineral matter. Consequently, he developed a series of hydroponics experiments, where by growing plants in sealed vials, in different types of water and weighing them regularly over the same time period, he could calculate how much biomass was gained over a set time period. He was able to draw a series of conclusions from these experiments by calculating the ratio of water lost to plant mass gained in the same period of time, thereby calculating the inverse of transpiration efficiency. This was probably the first time that the inverse of transpiration efficiency was calculated using experimental data. He showed that 50 to 700 times as much water was lost than biomass gained. He also reported that plants grown in water containing more terrestrial matter grew more and with less water consumed. From these observations, he concluded that water serves only as a vehicle for the terrestrial matter that forms vegetables and that vegetable matter is not formed out of water. He is still remembered more for his geological publications (Porter 1979 ) than for his contributions to botany (Stanhill 1986 ).

In his “history of ecology” series, Egerton ( 2004c ) nicely sums this period thusly: “each of these authors (Bacon, Boyle, Helmont, Sharrock) built upon the work of his predecessors and improved somewhat the understanding of plant growth and how to study it. However, they still fell short of a basic understanding of plant growth. Before that could be achieved, chemists would have to identify the gases in the air”. This series of studies shows that from the end of the seventeenth century onwards, experiments replaced speculation (Morton 1981 ), in botany as well as in many other areas of science.

From the end of the seventeenth century, the question of how plants grow was still unresolved, although it was known that nutrients were conducted from the roots in the ascending sap to the leaves. A major improvement in the understanding of how transpiration and its variations work was the discovery of cells by Robert Hooke towards the middle of the seventeenth century (Egerton 2005 ) and subsequently the discovery of stomata on leaf surfaces. One of the first to describe stomata may have been Malpighi in “Anatomy of Plants” (Malpighi 1675 in Möbius 1901 ). Based on Malpighi’s and Grew’s ( 1682 ) studies, John Ray suggested in “Historia Plantarum” (Ray 1686 in Lazenby 1995 ) that the apertures in the leaves, when open, would give off either breath or liquid. Ray may have been the first to have connected stomata with transpiration. He also suggested that the loss of water by evaporation is compensated constantly by water from the stem, and thus transpiration results from a constant water flux. He also observed that sap ascends the stems of trees in sap-bearing vessels which do not contain valves. He did, however, admit that it cannot be capillary forces that make water go up tall trees.

Ideas on photosynthesis developed slowly from the middle of the seventeenth century onwards. Malpighi ( 1675 ) suggested that leaves produce (“concoct and prepare”) the food of plants and from leaves this food passes to all parts of the plant. Similarly, Claude Perrault in “Essais de Physique” (Perrault 1680 ) defended the hypothesis that the root acts as the mouth of the plant and that the leaves serve to prepare the food arriving with the sap from the root so that it can be used in the rest of the plant. John Ray in “History Plantarum” (Ray 1686 in Lazenby 1995 ) concurs with this, however adding in “The wisdom of God” (Ray 1691 in Lazenby 1995 ) that “not only that which ascends from the Root, but that which they take in from without, from the Dew, moist Air, and Rain”. He also thought that light could play a role in this preparation of the plant sap. At this time, most authors (Malpighi, Perrault, Mariotte, Ray) knew about the circulation of sap, up as well as down, and that leaves served somehow to transform the upcoming sap into food for the plant.

In 1770 , Lavoisier published “Sur la nature de l’eau” (“On the nature of water”, translation by the author) and reviewed the literature on the possibility of water changing into earth to nourish plants. Lavoisier cited the Van Helmont experiment and later works which tested Van Helmont’s idea by growing plants in water (e.g. Boyle, however he did not cite Woodward). He was critical of the idea that it could be a transformation of water that would constitute plant material. This was based mainly on experiments by himself and others, showing even distilled water would contain traces of “soil”. However, he also defended the idea, based mainly on Charles Bonnet’s observations, that leaves absorb vapours from the atmosphere that contribute to plant growth.

Helmont had coined the term “gaz” in the mid-seventeenth century and had been able to distinguish different gazes from air (Egerton 2004a ). It was only in the middle of the eighteenth century that gases were studied in the laboratory and several observations by different researchers would finally lead to an understanding of respiration and photosynthesis (Tomic et al. 2005 ; Nickelsen 2007 ). Richard Bradley seems to be one of the first to clearly state (in letters from 1721 to 1724) that plant nourishment can be drawn from the air. Hales ( 1727 ) agreed with this theory, which was not yet widely accepted (Morton 1981 ), and suggested that light might be involved, which helped to pave the way for the discovery of photosynthesis. Black ( 1756 ) was able to identify carbon dioxide (which he called fixed air) using a lime water precipitation test. He demonstrated that this “fixed air” did not support animal life or a candle flame (Egerton 2008 ). Charles Bonnet ( 1754 ) made an important observation, i.e. branches with leaves that were submerged under water would produce air bubbles on their surfaces when sunlight shone on them, but not after sunset. Senebier refined these experiments in 1781 (Morton 1981 ), by showing that the leaves produced no oxygen in the sunlight when the surrounding water was free of carbon dioxide and that the rate of oxygen production was higher with carbon dioxide-saturated water. Tomic et al. ( 2005 ) present nicely the steps leading up to the term photosynthesis. This began with Priestley ( 1775 ) demonstrating that the air given off by animals and by plants was not the same, Ingen-Housz ( 1779 ) observed the important role of light, and the dispute between Senebier and Ingen-Housz from 1783 to 1789 resolved more clearly the functions of carbon dioxide emission (respiration) and absorption (photosynthesis). Based on these results and his own very detailed observations, de Saussure reported in 1804 that the carbon necessary for plant growth is absorbed mainly by green leaves from atmospheric carbon dioxide and he estimated that the largest part of the accumulated dry matter of plants is made of this carbon. Thus, the dispute of what the plant matter is made of that began in antique Greece was resolved at the end of the eighteenth century.

3 How much water do plants need to grow?

The late eighteenth century marked the beginning of applied agricultural science and the rise of plant physiology (Morton 1981 ). Work continued on transpiration and stomata, with a large number of experiments. Burgerstein ( 1887 , 1889 ) managed to assemble 236 publications on transpiration of plants from 1672 to 1886, citing short abstracts of each and comparing them critically. Also, Unger published in 1862 a major review article covering such subjects as the relationship of transpiration to temperature and humidity; daily cycles, including night; differences in adaxial and abaxial leaf surfaces; the impact on transpiration of type, number, size and distribution of stomata; the structure of the epidermis (cell layers, cuticle, hairs and wax); development of the mesophyll; size of intercellular spaces and cell turgor; and the impact of plant transpiration on the atmosphere (Unger 1862 in Burgerstein 1887 ). Scientists started to reflect on the interaction of plants, or more specifically their leaves, with their environment, and experimentation included the responses of stomata to light quantity (Möldenhawer 1812 ) and quality (Daubeny 1836 in Burgerstein 1887 ). Based on inconsistent observations by e.g. Banks, Möldenhawer and Amici, advances were also made on the functioning of stomata (Mohl 1856 ). However, progress was mainly based on a comment in von Schleiden ( 1849 ) that the state of the stomata would be the result of the water in- or outflow of the pore cells (called “Schliesszellen”) and he showed experimentally that stomata close when the pore cells lose water. As knowledge of transpiration, stomatal opening and their dependence on environmental variables increased, new questions arose about the water consumption of plants.

Another milestone along the way to understanding the transpiration of plants in the nineteenth century was the publication by Sir John Bennet Lawes ( 1850 ), “Experimental investigation into the amount of water given off by plants during their growth; especially in relation to the fixation and source of their various constituents”. He described experiments on wheat, barley, beans, peas and clover using differently fertilised soils. He was using plants in closed containers and an especially designed balance to “estimate the amounts of water given off” (Fig. 1 ). He observed increased evapotranspiration with higher temperatures during the growing season, and asked whether “this increased passage of water through the plants, carrying with it in its course many important materials of growth from the soil, and probably also influencing the changes in the leaves of these, as well as of those derived from the atmosphere, will not be accompanied with an equivalently increased growth and development of the substance of the plant”. This was followed by an important discussion of the influence of temperature on evaporation and growth as well as the resultant ratio. He discussed in the introduction “the relationship of the water given off to the matter fixed in the plants”; he gave his results in this ratio and in the inverse ratio, and applied these ratios to different scientific questions. The first ratio (transpired water divided by plant matter, the inverse of today’s TE) was used to interpret his results in terms of water use compared to field available water, and the latter’s ratio (plant matter divided by transpired water, equivalent to today’s TE) was used to discuss his results in terms of functional differences among species. From the observed functional differences, he concluded that there was “some definite relationship between the passage of water through the plants and the fixation in it of some of its constituents”. He was, thereby, introducing a new question about the link between dry matter accumulation and transpiration, which will be treated in the next chapter.

Illustration from Lawes ( 1850 , p. 43) of the special balance constructed for weighing plants in their “jars” to estimate the amounts of water given off and also the “truck” on which a series of jars was moved to the balance

Towards the end of the nineteenth century, research interest started to include agricultural questions of water use. Marié-Davy ( 1869 ) measured transpiration (standardised by leaf surface) of over 30 plant species, including eight tree or shrub species as well as herbaceous and agricultural plants. He estimated transpiration per soil area, thereby establishing that a prairie would transpire more than trees. von Höhnel ( 1879 ) estimated long-term transpiration of branches of 15 tree species (standardised on leaf surface or leaf dry weight). He used these data of branch transpiration to upscale to whole trees and concluded that compared to agricultural plants, the amount of rain seemed sufficient for tree growth. Hellriegel ( 1871 ) had already similarly concluded for cereals in the Mark Brandenburg (Germany) region that rainfall would not be sufficient, as had Marié-Davy ( 1874 ) for wheat in the Paris (France) region. In parallel with these more quantitative interrogations about water use, from the mid-nineteenth century, scientists started to ask more functional questions about the relationship between transpiration and dry matter accumulation, in a context of vigorous growth of botanical sciences and the complex relation between organisms and their environment (Morton 1981 ).

4 Are transpiration and dry matter accumulation linked?

Lawes ( 1850 ) had already reflected on a functional relationship between water flux and plant matter accumulation. In the following years, there were several publications on the transpiration of trees, and although no transpiration efficiency was estimated, the understanding of tree transpiration advanced. Many comparative studies were published. Lawes ( 1851 ) on “Comparative evaporating properties of evergreen and deciduous trees” considered twelve different tree species. He provided measurements of the variation in transpiration with temperature and hygrometry data. With these, he concluded that “evaporation is not a mere index of temperature but that it depends on vitality influenced by heat, light and other causes”. In the late nineteenth century, several researchers estimated and compared values of the ratio of transpiration and dry matter accumulation for different plants (Burgerstein 1887 ). With the growing evidence of variation in this ratio, scientists started to reflect on the relationship between transpiration and dry matter accumulation, aided by the development of new measurement techniques. A major question was if there would be a tight coupling between transpiration and dry matter accumulation, resulting in a constant transpiration efficiency, or if variation could be observed.

Dehérain ( 1869 ) studied evaporation and the decomposition of carbonic acid in leaves of wheat and barley. Using an ingenious apparatus, he was probably the first to directly measure evaporation of water in parallel with carbonic acid decomposition. He studied the effect of variously coloured light, and although he did not calculate the ratio between evaporation and carbonic acid decomposition, he did conclude that light of different colours had a similar effect on carbonic acid decomposition and on water evaporation from the leaves. His final conclusion was that “it is likely that there is existing between the two main functions of plants, evaporation and carbonic acid decomposition, a link, of which we need to determine its nature” (translation from the original French by the author). Several other scientists also commented on the relationship between transpiration and dry matter production. Fittbogen ( 1871 ) supposed, similarly to Lawes ( 1850 ) before him, but with more experimental evidence, that there should be a positive relationship between transpiration and production of dry matter. Dietrich ( 1872 in Burgerstein 1887 ) supposed that this relationship would be linear, whereas Tschaplowitz ( 1878 in Burgerstein 1887 ) introduced the idea that there should be an optimum transpiration at the maximum production of matter. Therefore, when the transpiration would increase over this optimum, this would lead to a decrease in assimilation rate. He was one of the first to suggest a non-linear relationship between transpiration and assimilation. Sorauer in “Studies on evaporation” ( 1880 ) defended the hypothesis that transpiration was not only a physical phenomenon but was also physiological. He stated that “It is not possible as yet to study the plant internal processes which regulate the transpiration, however it is possible to quantify the relationship between dry-matter and transpiration” (translation from German by the author), suggesting thereby TE as a means to advance the understanding of plant internal processes. Sorauer was probably at the cutting edge of science of his time. He pointed out specifically that variability among plants of one species was due to genetics (German, “erbliche Anlagen”), a startling and even daring assertion for his time. He asserted that for comparative studies, genetic variability needed to be minimised. To achieve this, he used, when possible, seeds from the same mother plant, grown in the same environmental conditions and a large number of repetitions. Using these protocols, he was probably one of the first to estimate TE on tree seedlings, showing that there was within species diversity in transpiration and growth, but that their ratio was more constant. He concluded from experiments on pear and apple trees that the pear trees used less water for the same biomass growth. He was able to go one step further and demonstrate that this difference was due to less transpiration per leaf area. By comparing different woody and herbaceous plants with different growth types, he postulated that when plants had a small leaf area combined with high transpiration, they had either a very strong growth increment, a high dry matter percentage, or a large root system. Overall, he observed relationships between dry matter production and transpiration; he concluded that there must be some regulation of the transpiration per unit leaf area by the co-occurring dry matter production.

Hellriegel ( 1883 ) argued that one cannot estimate a constant ratio between transpiration and production as there were factors which influence each independently. He also commented that it might make sense to estimate mean values of transpiration for various agricultural plants, as this would be for practical and scientific value. He thought that the most logical standardisation would be by the mass of the dry matter produced during the same time period. He called this “relative Verdunstungsgrösse” which can be translated into English as “relative transpiration”. He was probably one of the first to give a name to the ratio between whole plant transpiration and dry matter production. He proposed a theory that for a long-term drought, plants would acclimate their morphology to decrease their “relative transpiration”. He provided additional experimental evidence that barley had decreased in relative transpiration over as many as seven levels of soil water deficit, relative to field capacity. Using his own observations, he proposed that when calculating a mean “relative transpiration” for a single species, variation of transpiration should be minimised and that plants should be tested together only under optimal conditions. Given the relatively small differences in relative transpiration that he observed among different crops, Hellriegel suggested that these differences would not explain why some crops grow better in wet locations and others on dry locations. Hellriegel was thus probably one of the first scientists to point out that the relationship between drought adaptation and “relative transpiration” might not be straightforward.

Understanding how biomass and water loss were connected was studied by Iljin ( 1916 ) on a newly detailed level. He measured simultaneously water loss and carbon dioxide decomposition and reported his data as grammes of water lost per cubic centimetre of carbon dioxide decomposed. He concluded from studying more than 20 plant species that “...it is generally agreed that the rates of water loss and of CO 2 assimilation are directly proportionate to stomatal aperture, and that consequently there exists a close connection between these two processes”.

At the end of the nineteenth century, the ratio of transpiration versus dry matter accumulation was recognised as an important plant trait, which varies among and within species in a complex interaction of each component with the other and with environmental factors.

5 How do plants differ in water requirement and how do they respond to variations in environmental factors?

In the late nineteenth century, several researchers estimated and compared values of the ratio of transpiration and dry matter accumulation for a range of cultivated plants (Fittbogen 1871 ; Dietrich 1872 ; Farsky 1877 , cited in Burgerstein 1887 ), giving evidence of the growing interest of agricultural scientists. The number of studies of transpiration efficiency greatly increased, thereby driving a new standardisation in terminology. King ( 1889 ) studied the inverse of transpiration efficiency and described it as “the amount of water required for a ton of dry matter”, and promulgated this terminology by using it in the titles of his publications between 1892 and 1895. Similarly, Leather ( 1910 ) published “Water requirements of the crops of India”, in which he defined the “transpiration ratio” as “the water transpired to the weight of dry plant produced”. The shift from a purely descriptive use of “water requirement” to a clearly defined one was provided by Kearney and Shantz ( 1911 ) as “… the degree to which a plant is economical in its use of water is expressed in its water requirement, or the total quantity of water which it expends in producing a pound of dry matter”. The term “water requirement” is the inverse of the modern transpiration efficiency, and was used by a rapidly increasing number of publications which were published on the water use of crops in the early twentieth century. Montgomery ( 1911 ) may have been the first to use the term for a plant trait in “Methods of determining the water requirements of crops”.

At the beginning of the twentieth century, the importance of gaining knowledge on the water requirements of plants can be seen in the technical effort that went into the measuring equipment. von Seelhorst ( 1902 ) presented a system of growing boxes on rails, placed belowground, including the balance, so that the top of the growing boxes was at the same level as the surrounding soil (Fig. 2 ). In the now well-known studies on “The water requirement of plants. I. Investigations in the Great Plains in 1910 and 1911”, Briggs and Shantz ( 1913a ) measured the water requirement for 21 crop and weed species, sometimes for different varieties of the same crop and under controlled and field conditions. In the same year, they reviewed the available literature on water requirement (Briggs and Shantz 1913b ), increasing their dataset to 31 different crop species. They discussed in detail studies from 29 different authors, many of which had only published once or twice on this subject. A few researchers were notable for their number of publications on the water requirement of crop plants: King with 6 publications between 1889 and 1905, and von Seelhorst with 9 publications between 1899 and 1907. The largest contributions came from Hellriegel ( 1883 ; 10 species) and Leather ( 1911 ; 15 species). Kiesselbach ( 1916 ) also reviewed 59 publications from 1850 to 1915 “which had studied transpiration in relation to crop yield, based upon plants grown beyond the seedling stage”. There were regular publications of original work from 1870s onwards, with more than one publication per year from 1890 onwards. The difference among species and the impact of environmental factors on water requirement was one of the main questions raised. These reviews and the increasing amount of newly published work per year are evidence of the growing interest in the “water requirement” of plants as a trait of increasing importance in agricultural sciences.

Illustration from von Seelhorst ( 1902 ), showing the quite sophisticated outdoor installation “Vegetationskasten” (growing boxes, translations by the author) to weigh plants in small waggons, with a “Kastenwagen” (boxwaggon), b “Waagebalken” (scale beam), c “Deckbretter” (cover board) and d “Waagentisch” (weighing table)

With regard to species differences in water requirement among crops, Schröder ( 1895 , cited in Maximov 1929 ) found two groups, among seven cereals, which differed in water requirement by a factor of 2. Millet, sorghum and maize were known to be drought resistant, and showed a lower water requirement than the remaining plants. These differences were confirmed by Kolkunov ( 1905 , cited in Maximov 1929 ), Briggs and Shantz ( 1914 ), Briggs and Shantz ( 1917 ) and Shantz ( 1927 ). Millet, sorghum and maize are now known to use the C4 carbon pathway of photosynthesis.

With regard to external environmental influences on plants, Briggs and Shantz ( 1913b ) distinguished between soil, atmosphere and plant factors. Soil factors which were investigated were soil moisture content, soil type, cultivation, soil volume, soil temperature, effect of fertilisers in soil or water cultures and effect of previous crops. Weather factors considered were air temperature and humidity, shade and carbon dioxide content. Other factors studied in direct relationship to the plants were parasite attacks, relative leaf area, cutting frequency, defoliation, planting density and the age of plants.

A critique of the term “water requirement” was not long in coming. Dachnowski ( 1914 ) wrote, “It is assumed by many writers that a definite and quantitative relation exists between transpiration and growth, and that hence the ratio of the weight of water absorbed and transpired by a plant during its growth to the green or dry substance produced is an adequate and simple measure of growth.”, followed by an argument why this was not the case.

6 Why do plants differ in transpiration efficiency?

The adaptations of plants to dry environments were an important ecological topic at the beginning of the twentieth century, as the discipline of “physiological ecology” (Iljin 1916 ; Moore 1924 ) began to develop. Iljin ( 1916 ) studied more than 20 different plant species in situ from different ecological locations, e.g. wet bottom soils and variously facing slopes of ravines with different aspects. Iljin proposed that “the water requirements of the different species should be very different, and consequently the amounts of water available should differently affect their processes of life”. Using his observations, he was able to show that “… in no case was the water loss per unit of decomposed CO 2 found to be equal to or more in xerophytes than in mesophytes”, thus suggesting a higher transpiration efficiency. He argued that mesophytes would have to close stomata “… in dry places in order to reduce evaporation, thus diminishing the rate of assimilation as well, whereas in the case of xerophytes, which are adapted to extreme conditions of existence, assimilation in similar circumstances proceeds actively”. He then tried to confirm his hypothesis by transplanting mesophytes from wetter sites to the drier environment of xerophytes. Iljin showed experimentally that in all cases, a higher water requirement was measured for mesophytes transferred to a drier site compared to their original site and compared to xerophytes at the dry site. He interpreted his observations as “plants growing in dry places are adapted to a more economical consumption of water”. He held this to be true for among- and within-species variation.

A milestone in forest “physiological ecology” was Bates’ ( 1923 ) study of the physiological requirements of Rocky Mountain trees. Bates wrote that for foresters, knowledge of demands of tree seedlings for moisture, light, heat and soil fertility was important for planning reforestation. He started a large investigation of six forest tree species, combining field studies to describe ecosystems, with experiments in controlled environments in order to determine species differences in relative transpiration and other water flow-related traits. Bates concluded from the comparison among species that trees of low water requirement would be trees that have a superior control over their water supply. He was however critical of a direct relationship between water requirement and drought resistance in trees. Moore ( 1924 ) commented that in correlating physiological measurements with the habitat characterisation of the species, Bates “... has opened new fields to forest investigations”. He also stressed that the results were counterintuitive in that the most xerophytic species had the highest water requirement, whereas the most mesophytic species had the lowest water requirement.

A similar discrepancy was observed by Maximov ( 1929 ) in the chapter “Efficiency of transpiration” in his book The Plant in relation to water , which was translated from Russian into English rapidly after its publication. Maximov preferred “efficiency of transpiration” to “water requirement”, arguing that the former would be more logically correct, because the determining process (transpiration) should be in the denominator, which also would have the effect that “… an increase in the figure denoting the value of the ratio actually corresponds to an increase of the efficiency per unit of water used”.

In his book, Maximov ( 1929 ) described experiments done at Tiflis Botanic garden (today in Georgia) by Maximov and Alexandrov ( 1917 ), where they studied local xerophytes for 3 years. They found xerophytes with a high efficiency of transpiration, particularly drought-resistant annuals. They also found that plants with a low efficiency of transpiration appeared to be the most typical semi-arid xerophytes. The mesophytes all displayed a medium efficiency. Maximov noted from other observations on the same plants that the “… majority of xerophytes with a low efficiency of water expenditure possess very extensive root systems, far exceeding in length the sub-aerial portions of the plant”. He also observed that these plants showed a strong transpiration and that this transpiration might constitute the “pump” which could draw water through such an extensive root system. He also observed that “members of the group of annual xerophytes with a high efficiency of transpiration are characterised by a relatively large leaf surface, which develops very rapidly”. He argued that this would confer a high intensity of assimilation. From these observations, he concluded a “lack of direct proportionality between efficiency of transpiration and the degree of drought resistance”, but also that “the magnitude of the efficiency of transpiration affords one of the most satisfactory tests of the ecological status of a plant”. Maximov applied the ecological classification developed by Kearney and Shantz ( 1911 ), which they had based on plants of the arid and semi-arid regions of North America: (1) drought-escaping with an annual growth cycle restricted to favourable conditions; (2) drought-evading, delay by various means the exhaustion of soil moisture; (3) drought-enduring, can wilt or dry but remains alive; and (4) drought-resisting, can store a water supply. It should be noted that the ecological definitions behind these concepts have changed with time and are used slightly differently today. Shantz ( 1927 ) argued that many of the drought-evading plants had a low water requirement and Maximov noted that this group included the highly efficient xerophytes with a large leaf area. Maximov also observed that xerophytes from the third group (drought-enduring) could show a very low efficiency of transpiration and belonged to the group of xerophytes with large root systems. Without concluding directly, he suggested a relationship between the transpiration efficiency of a xerophyte and its ecological strategy when facing limited soil water content. These studies by Maximov are among the most complete concerning the relationship between a plants’ resistance to drought and their transpiration efficiency, reflecting the interest of scientists in ecological questions of plant functioning, especially in relation to drought.

Although work on crop plants advanced greatly in the early twentieth century, results were scarcer for tree species. Raber ( 1937 ) concluded his book on “Water utilization by trees, with special reference to the economic forest species of the north temperate zone” with detailed discussions of available data for forest trees. He commented that “much more work on the water requirements of trees of all ages and under varying site conditions is needed”. And he continued that “In view of the importance of planting drought-resistant species in regions where the water supply is below the optimum for most tree species, it is extremely urgent to know more about what qualities make for drought resistance and what species possess these qualities to the greater degree.” These conclusions by Raber show that from the beginning of the twentieth century, the estimation of transpiration efficiency had taken an important place in ecological studies on forest tree species, however not without some critical thoughts on the subject.

7 What is the functional importance of transpiration?

Already in the 1870s and 1880s, the role of stomata in the diffusion of carbon dioxide into the leaf (during the day) and out of the leaf (during the night) was discussed in the scientific literature, as shown by the extensive literature review by Blackman ( 1895 ) (see also section 4 above). Especially the functional importance of transpiration was an open question. There were two opposing lines of thought. As summarised by Iljin ( 1916 ), one defended the line of inquiry that transpiration was important only in the process of transporting mineral salts from roots to leaves; the other held that the opening of stomata was necessary for absorbing the carbonic acid from the atmosphere, which leads to a loss of water and is described as an “inevitable evil”. Iljin ( 1916 ) preferred the second line of investigation and attributed a major role to the stomatal aperture, which controlled both the absorption of carbonic acid from the atmosphere and the loss of water. He concluded that in “physiologico-ecological” investigations, assimilation should be studied together with transpiration. Maskell published a series of papers in 1928, where especially “XVIII.—The relation between stomatal opening and assimilation.” (Maskell and Blackman 1928 ) used an apparatus to estimate apparent CO 2 assimilation and transpiration rate in parallel (Fig. 3 ), and was therefore able to study in detail their interdependence, developing the first mathematical descriptions, based on the development of the theories about the diffusion of gases (Brown and Escombe 1900 ). Methodological advances intensified research on the leaf-level relationship between assimilation and transpiration and allowed the study of plant functioning in more detail. The major step forward was the construction of an infrared gas analyser (URAS: in German “Ultrarotabsorptionsschreiber”, IRGA, infrared gas analyser) by Lehrer and Luft in 1938 (Luft 1943 ) at a laboratory of BASF, IG Farbenindustrie. Normally used in industry and mining, Egle and Ernst ( 1949 ) may have been the first to describe the use of the URAS for plant physiological measurements. By 1959, the URAS was routinely used for measuring stomatal resistance or transpiration in parallel and simultaneously with CO 2 assimilation, on the same leaf (Rüsch 1959 ). This was a great improvement on previous methods and led rapidly to a set of equations for calculating assimilation and stomatal conductance (Gaastra 1959 ).

Two figures taken from Maskell and Blackman ( 1928 ): on the top, Figure 1 (p. 489) showing a “Combined assimilation chamber and porometer for simultaneous investigation of apparent assimilation and stomatal behaviour. A. Section of leaf chamber passing through porometer chamber. B. Back view of leaf chamber showing also air-flow meter attached by pressure tubing to porometer and to leaf chamber”. On the bottom, Figure 5 (p. 497) “Relation between porometer rate and apparent assimilation at ‘high’ light, December 1920.” Exp t LI and LII correspond to 2 days of continuous measurements to what Maskell called “diurnal march”

Scarth ( 1927 ) argued that there would be little advantage for a plant to have a high rate of transpiration, but stressed the “... advantage of maintaining the fullest diffusive capacity of the stomata and the highest possible pressure of CO 2 in the intercellular spaces”. He concluded that the principal function of stomata “... is to regulate that very factor which is presumed to regulate them, viz. the concentration of CO 2 in the leaf or, respectively, in the guard cells”. Maskell and Blackman ( 1928 ) tested this hypothesis experimentally and concluded that the rate of uptake of carbon dioxide was determined by variations in stomatal resistance and by resistances within the leaf, thereby introducing the importance of the CO 2 concentrations in the chloroplasts. The suggestion of a strong link between the leaf internal carbon dioxide concentration and leaf-level WUE represented a large advance in the theoretical understanding of WUE.

Penman and Schofield ( 1951 ) proposed, perhaps, the first theoretical link between the leaf-level transpiration ratio (leaf transpiration divided by assimilation) and the ratio of the coefficients of diffusion of water vapour and carbon dioxide in air, and the water vapour and carbon dioxide air-to-leaf pressure gradients. Gaastra ( 1959 ) suggested that the leaf internal conductance to carbon dioxide is a pivotal point of the ratio of assimilation to transpiration and of the water economy of crop plants. Bierhuizen and Slatyer ( 1965 ) showed that the transpiration ratio could be predicted from water vapour and carbon dioxide gradients over a range of light intensities, temperatures and relative humidities. These studies were the first to suggest that whole plant transpiration efficiency might be regulated directly by leaf functioning and would be therefore a trait in its own right and not only the ratio of two plant traits.

8 How can the transpiration ratio be improved?

Because water is increasingly scarce in a warming world, Rüsch ( 1959 ) queried whether the luxury of highly transpiring tree species could be justified. He argued for selective breeding of tree species varieties with low transpiration-to-assimilation ratio T/A by means of minimising transpiration while maximising assimilation. Also Polster et al. ( 1960 ) assessed the potential suitability of tree species to sites by their dry matter production and transpiration ratio. Troughton ( 1969 ) and Cowan and Troughton ( 1971 ) suggested that genetic selection of plant varieties could be used to improve the transpiration ratio by decreasing leaf internal resistance to carbon dioxide diffusion. Cowan and Farquhar ( 1977 ) built on this theme by proposing that stomata might optimise carbon gain to water lost by varying the conductances to diffusion and thereby maximising the ratio of the mean assimilation rate to mean rate of evaporation in a fluctuating environment. Approaches which target photosynthesis, stomatal opening, leaf internal resistance to carbon dioxide diffusion or stomatal optimisation in order to improve plants performance have since been followed in plant breeding and have largely been reviewed elsewhere (e.g. Condon et al. 2004 ; Cregg 2004 ; Vadez et al. 2014 ).

9 Intrinsic water use efficiency and carbon stable isotopes

Another milestone towards contemporary research on water use efficiency was the use of stomatal conductance to water vapour rather than transpiration by Farquhar and Rashke ( 1978 ) and to calculate water use efficiency as assimilation divided by stomatal conductance. This definition allowed an estimation of water use efficiency resulting only from plant functioning, without a direct impact from leaf-to-air vapour pressure difference and was named by Meinzer et al. ( 1991 ) “intrinsic water use efficiency” (W i ). Knowledge of W i facilitated the search for a genetic basis of within species variation, e.g. Brendel et al. ( 2002 ), Condon et al. ( 2002 ) and Chen et al. ( 2011 ).

Development of the stable carbon isotope method for estimating W i resulted in a widely applicable screening method, and a large increase of publications around plant water use efficiency. Based on the two-step fractionation model (atmospheric CO 2 – leaf internal CO 2 – plant carbon) proposed by Park and Epstein ( 1960 ), various models explaining the difference in carbon isotope composition between atmospheric CO 2 and plant carbon were developed in the late 1970s and early 1980s, e.g. Grinsted ( 1977 ), Schmidt and Winkler ( 1979 ) and Vogel ( 1980 ). Vogel’s model contained many theoretical aspects which, however, lacked experimental understanding. In parallel, Farquhar ( 1980 ) developed a similar model, but which resulted in a simple, elegant mathematical equation relating plant natural abundance carbon isotope discrimination, relative to atmosphere, to the ratio of leaf internal to atmospheric CO 2 concentration. This was, in turn, related to W i . Experimental evidence showed that carbon isotope measurements, in wheat, reflected long-term water use efficiency (Farquhar et al. 1982 ) as well as whole plant transpiration efficiency (Farquhar and Richards 1984 ). They concluded that carbon isotope discrimination may provide an effective means to assess and improve WUE of water-limited crops. Strong correlations between whole plant TE and stable carbon isotope measurements of plant organic material were shown in a host of papers to be. Some of these papers were (1) for crops and other annuals (Hubick et al. 1986 ; Ehleringer et al. 1990 ; Virgona et al. 1990 ) and (2) for trees (Zhang and Marshall 1994 ; Picon et al. 1996 ; Roupsard et al. 1998 ). The isotopic method has spread rapidly as a general estimator of WUE and continues to be used widely in screening programmes for plant improvement as well as in ecological research, e.g. Rundel et al. ( 1989 ) and notably used in tree rings (McCarroll and Loader 2004 ).

10 Closing remarks

Water use efficiency is probably one of the oldest of plant traits to stimulate across the centuries the interest of philosophers, theologians, Middle Age savants, natural philosophers and modern plant scientists across different disciplines (plant physiology, ecophysiology, ecology, genetics, agronomy). The interest began as a purely philosophical one, progressed to thought experiments, towards an interest in plant functioning and its relationship to the environment.

Already in the early Renaissance (mid-fifteenth century), an experimentation was proposed, in a time when botany consisted mainly of naming plants (Morton 1981 ). It is then also an early example of an actually performed experimentation, the famous willow experiment by Van Helmont ( 1662 ) as well as of early “in laboratory” experimentation on plants (hydroponics experiments by Woodward 1699 ). The question of what makes plants grow, between water and soil, kept natural philosophers busy up to the end of the eighteenth century, when the assimilation of CO 2 was discovered and the question finally solved.

Early in the nineteenth century, the interest and experimentation turned to the amount of water that plants would need to grow, in the context of a developing research on agricultural practices (Morton 1981 ). Biomass was used to standardise the water losses which allowed comparisons among species (crops as well as trees) and a beginning study of the impact of different environmental variables.

At the end of the nineteenth century, knowledge on the physiological aspects of CO 2 assimilation and the control of transpiration by stomata had sufficiently advanced, so that scientists started to reflect on their inter-dependency. Was transpiration only a physical process or was there a physiological control? Was transpiration regulated by the dry matter production? Or does the stomatal opening determine the rate of CO 2 assimilation?

At the turn of the twentieth century, the study of species differences led to questioning why these differences did exist. As the discipline of “physiological ecology” developed, “water requirement” was inverted into an “efficiency”, reflecting an evolution from standardising transpiration to a trait in its own right. This introduced ecological questions about the adaptation of plants to dry environments and the relation to transpiration efficiency. Counterintuitive results stimulated the discussion and linked differences in WUE to different ecological strategies.

Methodological and theoretical advances in the description of leaf gas exchange in the mid-twentieth century showed the central role of stomata in the control of transpiration and CO 2 assimilation, leading to the idea that stomata might optimise water losses versus carbon gain. The development of carbon stable isotopes as an estimator of leaf-level WUE was an important step not only to further develop these theoretical considerations, but also towards large-scale studies. In parallel, modelling approaches were developed to scale from leaf-level WUE to whole plant TE, e.g. Cernusak et al. ( 2007 ), and to the field or canopy, e.g. Tanner and Sinclair ( 1983 ).

At least from the beginning of the twentieth century onwards, also critical views on the relationship between water requirement and its relation to growth mostly in terms of yield were published (Dachnowski 1914 ). Viets ( 1962 ) asked “Is maximum water use efficiency desirable?”, especially in terms of crop production. Sinclair et al. ( 1984 ) considered different options for improving water use efficiency, however concluding that most of these have important limitations or drawbacks. This discussion is ongoing, as can be seen by the article published by Blum ( 2009 ): “Effective use of water (EUW) and not water-use efficiency (WUE) is the target of crop yield improvement under drought stress”.

Exploration and application of transpiration efficiency at the whole plant level, and its derivatives at other levels, are still a very active research field across nearly all levels of forest science: concerning very rapid processes at the leaf level (Vialet-Chabrand et al. 2016 ), up-to-date genetic and genomic approaches for breeding (Plomion et al. 2016 ; De La Torre et al. 2019 ; Vivas et al. 2019 ), studying local adaptation of trees to their environment in a population genetic context (Eckert et al. 2015 ) or an ecological context (Pellizzari et al. 2016 ), water use efficiency from the plant to the ecosystem (Medlyn et al. 2017 ), estimated at the population level (Rötzer et al. 2013 ; Dekker et al. 2016 ) or modelling up to the global earth level (Cernusak et al. 2019 ), just to name a few. Thus, the first curiosity of Greek philosophers has motivated scientists through history, with many exciting discoveries still to come.

Change history

17 june 2021.

A Correction to this paper has been published: https://doi.org/10.1007/s13595-021-01073-0

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Acknowledgements

Much of the historical background is based on A.G. Morton’s “History of Botanical Sciences” as well as to Frank N. Egerton’s “A History of the Ecological Sciences” series in the “Bulletin of the Ecological Society of America”. The author is also largely indebted to C. Schuchardt from the Library of the Staatsbetrieb Sachsenforst for help with the quest for rare German publications. The author would also like to thank E. Dreyer and J.M. Guehl (both from the SILVA Unit at INRAE Nancy, France) who commented extensively on an earlier version of the draft and J. Williams (University of Sussex), L. Handley and J. Raven (University of Dundee) who made many valuable suggestions and improved language.

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Brendel, O. The relationship between plant growth and water consumption: a history from the classical four elements to modern stable isotopes. Annals of Forest Science 78 , 47 (2021). https://doi.org/10.1007/s13595-021-01063-2

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Absorption of Water In Plants

Absorption of water in plants is a vital process that is important for plant growth and other metabolic activities. Water absorption in lower plants takes place by the process of osmosis through the whole plant body . In higher plants, the mechanism of water absorption is through the root hairs .

Plants mainly absorb water from the soil by the capillary action . There are five types of water that are found in the soil, namely runway water, gravitational water, hygroscopic water, chemically combined water and capillary water. Among the runaway water, gravitational water, hygroscopic water, chemically combined water, only the capillary water is useful for the plant.

There are some epiphytic plants, which grow on the substratum like rock and soil, while other plants absorb water by their aerial roots . The total water content in the soil is called holard . The water content consumed by the plant is called chesord. Water unconsumed by the plant is called echard .

Content: Absorption of Water In Plants

• Types of water absorption in plants
• Role of root hairs in water absorption
• Mechanism of water absorption in plants
• Factors affecting water absorption in plants

Absorption of water in plants is a biological process, in which the plants uptake capillary water from the soil to the root xylem through the root hairs during various plant processes like respiration, transpiration and osmosis. The water supply is an important factor, which directly or indirectly influences all the plant activities such as photosynthesis, internal water balance etc.

Loss of water in plants may result in loss or turgor, leaf-wilting, closure of stomata, reduction in photosynthetic activity and protoplasm disorganization. In plants, the absorbed water typically exists in two phases, namely apoplastic and symplastic water. Apoplastic water resides with the cell wall and xylem components, whereas symplastic water remains in the cell protoplast.

• Firstly, the two types (active and passive water absorption) were introduced by the scientist named Renner in 1912-1915.
• After the types of water absorption, two theories were introduced to know more about the concept of active absorption of water.
• The osmotic theory was given by the two scientists Atxins and Priestley .
• The non-osmotic theory was given by Bennet , Clark and Thimann in 1951.

Types of Water Absorption in Plants

Plants typically absorb water by the following two methods:

• Active absorption of water
• Passive absorption of water

Active Absorption of Water

This type of water absorption requires the expenditure of metabolic energy by the root cells to perform the metabolic activity like respiration. Active absorption in plant occurs in two ways, namely osmotic and non-osmotic absorption of water.

• Osmotic active absorption of water : In this type, the water absorption occurs through osmosis where the water moves into the root xylem across the concentration gradient of the root cell. The osmotic movement is due to the high concentration of solute in the cell sap and low concentration of the surrounding soil.
• Non-osmotic active absorption of water : Here, the water absorption occurs where the water enters the cell from the soil against the concentration gradient of the cell. This requires the expenditure of metabolic energy through the respiration process. Hence, as the rate of respiration increases, the rate of water absorption will also increase. Auxin is a growth regulatory hormone, which increases the rate of respiration in plants that, in turn, also increase the rate of water absorption.

Passive Absorption of Water

This type of water absorption does not require the use of metabolic energy. The absorption occurs by metabolic activity like transpiration. Passive absorption is the type where the water absorption is through the transpiration pull. This creates tension or force that helps in the movement of water upwards into the xylem sap. Higher is the transpiration rate, and higher is the absorption of water.

Role of Root Hairs in Water Absorption

Root cells, nucleus, and vacuole or cell sap are present inside the cytoplasmic membrane. Soil aggregates contain small droplets of water carried away by the root hairs into the root xylem through different mechanisms, out of which osmosis is most common.

Mechanism of Water Absorption in Plants

The movement of water from the soil to the root xylem occurs through the following stages:

• In the first step, the root hairs of the plant will absorb the water from the surrounding soil through the process of osmosis. The soil has high water concentration than the cell sap. Therefore, the water will move from a high concentration to the low concentration following osmosis through the cytoplasmic membrane of the root hairs.
• After entering into the root hair, the water will cross the epidermis or piliferous layer of the root system.
• Then, the water will move from the epidermis to the root cortex .
• From the root cortex, the water will travel through the endodermis that consists of suberic and passive cells. The further movement of water is facilitated by the passive cells.
• Then, water moves from the pericycle to the root xylem, i.e. perixylem and metaxylem. Water will be stored in the xylem root system, which can be utilized by the plant body to perform various metabolic activities and for its growth.

Factors Affecting

There are two kinds of factors that directly or indirectly influence the activity of water absorption.

Extrinsic factors: It includes external factors or environmental factors like:

• Soil water : Soil carries five different types of water, out of which the capillary water is useful for the biological activity of the plant.
• The concentration of soil solution : The concentration of soil must be less. If there is a high concentration of soil, then it will be called physiologically dry soil. Highly concentrated or dry soil makes the water absorption difficult.
• Soil air : There should be space between the soil particles for the proper air supply. If the quantity of oxygen is less, then the quantity of carbon dioxide will be more, which leads to the anaerobic respiration.
• Soil temperature : The optimum temperature is 20- 35 degrees Celsius.

Intrinsic factors : It involves the metabolic activities like respiration , transcription and the number of root hairs which directly influences the rate of water absorption.

Therefore, water absorption in plants occurs through the root hairs that carry the water present in the soil and forms a zone called the root hair zone. The root hairs absorb water through their wall, which is water-loving “Hydrophilic” in nature. Therefore, the high permeability of root hairs to the water will help in uptake water either through osmosis or transpiration.

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Agriculture in India

Essay on water potential in plants | plant-water relationships | agronomy.

Here is an essay on ‘Water Potential in Plants’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Water Potential in Plants’ especially written for school and college students.

Essay on Water Potential in Plants

Essay Contents:

• Essay on the Measurement of Plant-Water Potential

Essay # 1. Meaning of Water Potential in Plants:

The chemical free energy of water in its purest form is also called water potential (Ψ W ). Purest form means there are no other molecules in it. The chemical energy is maximum and its value is given as 0 bars. Addition of solutes to pure solvent decreases the chemical free energy of pure water, because certain amount of energy of a number of water molecules is used for binding to the surface of solutes.

So the total value of water potential of a solution is less than zero; it is always expressed in negative pressure values. Here, it is equal to DPD; if the water potential of pure water is zero and DPD is also zero. But the water potential of solution is less than zero expressed in negative value, but DPD of the solution is expressed in positive value.

These energy relations are governed by the said equations, understanding of it is very important:

Ψ w = Ψ s + Ψ p + Ψ g

where, Ψ w = water

Ψ s = Solutes – Solute potential or osmotic potential

Ψ p = Pressure – hydrostatic pressure of the solution, it is often called turgour pressure, which can be negative or positive

Ψ g = Gravity – will not be considered for normal calculations.

Pure water: Ψ p = 0 MPa

Ψ s = 0 MPa

Ψ w = Ψ p + Ψ s = 0 MPa

DPD of pure water = 0 bars; DPD of a solution = (+) bars

Ψ sw of pure water = 0 bars; Ψ w of a solution = (-) bars

Water potential of pure water in an open container is zero because there is no solute and the pressure in the container is zero. Adding solute lowers the water potential. When a solution is enclosed by a rigid cell wall, the movement of water into the cell will exert pressure on the cell wall. This increase in pressure within the cell will raise the water potential (Fig 5.1).

Water potential (Ψ) = Pressure potential (Ψ P ) + Solute potential (Ψ s )

Water potential is the measure of potential energy in water and drives the movement of water through plants.

Key Points :

1. Plants use water potential to transport water to the leaves.

2. Water potential is a measure of the potential energy in water as well as the difference between the potential in a given water sample and pure water.

3. Water potential is represented by the equation:

Ψ W = Ψ s + Ψ p + Ψ g + Ψ m

4. Water always moves from the system with a higher water potential to the system with lower water potential.

5. Solute potential (Ψ s ) decreases with increasing solute concentration; a decrease in Ψs causes a decrease in the total water potential.

6. The internal water potential of a plant cell is more negative than pure water; this causes water to move from the soil into plant roots via osmosis.

Water potential is a measure of the potential energy in water or the difference in potential energy between a given water sample and pure water (at atmospheric pressure and ambient temperature).

Water potential is denoted by the Greek letter Ψ (psi) and is expressed in units of pressure (pressure is a form of energy) called Megapascals (MPa). The potential of pure water (Ψ w pure H 2 O) is designated a value of zero (even though pure water contains plenty of potential energy, that energy is ignored). Water potential values for the water in a plant root, stem or leaf are, therefore, expressed in relation to Ψ w pure H 2 O.

Water potential in plant solutions is influenced by solute concentration, pressure, gravity and factors called matrix effects.

Water potential can be broken down into its individual components using the following equation:

Ψ t = Ψ s + Ψ p + Ψ g + Ψ m

where, Ψ s = Solute potential

Ψ p = Pressure potential

Ψ g = Gravity potential

Ψ m = Matric potential.

As the individual components change, they raise or lower the total water potential of a system. When this happens, water moves to equilibrate, moving from the system or compartment with a higher water potential to the system or compartment with a lower water potential. This brings the difference in water potential between the two systems (Δ) back to zero (Δ = 0).

Therefore, for water to move through the plant from the soil to the air (transpiration), the conditions must exist as such:

Ψ soil > Ψ root > Ψ stem > Ψ leaf > Ψ atmosphere.

Water only moves in response to Ä, not in response to the individual components. However, because the individual components influence the total Ψ system , a plant can control water movement by manipulating the individual components (especially Ψ s ).

Essay # 2. Plant-Water Relations New and Old Terminology :

Water relations in plant cell can be described in old set of terminology: diffusion pressure deficit (DPD), osmotic pressure (OP) and turgor pressure (TP) or in terms of new terminology. Water potential (Ψ) concept is the new term for DPD. Both DPD and V are numerically equal but are opposite in algebraic sign.

Ψ = (-) DPD

Similarly osmotic potential (Ψ s ) is numerically equal to osmotic pressure.

Ψ s = (-) OP

Turgor pressure is referred to as turgor potential (Ψ p ) which is not only numerically equal to TP but similar in algebric sign also.

Metric pressure (MP) is usually neglected but under new terminology (Ψ m ) it exists in the following relationship:

(Ψ m ) = (-) MP

When plasmolised cell is placed in pure water, it absorbs water and cell wall gradually increases as the vacuole swells in size and at a certain point plasmalemma exerts pressure on cell wall, the turgor pressure. Thus turgor pressure is a centrifugal pressure exerted by cytoplasm and cell membrane on cell wall.

Using old terminology, water status of the cell is described as DPD and its contributing pressure as follows:

DPD = OP – TP

DPD = OP, when TP = 0

The same situation is explicable in new terminology and water potential equation.

Ψ = (Ψ s ) + (Ψ p ) + (Ψ m )

Ψ = Ψ s + Ψ p when Ψ m is negligible

Ψ = Ψ s when Ψ p is zero.

It is important to keep notice of algebric signs while attempting data handling and numerical problems.

(-)Ψ t = (-) (Ψ s ) + (+) (Ψ p ) + (-) (Ψ m )

Essay # 3. Determination of Plant-Water Potential:

Energy status of plant cells is determined by three/four major factors:

1. Ψ s = Solute potential

2. Ψ p = Pressure/turgor potential

3. Ψ m = Matric potential

4. Ψ g = Potential due to gravity.

Total plant-water potential can be expressed, in terms of its component potentials, as indicated below:

Ψ w = Ψ s + Ψ p + Ψ m + Ψ g

1. Ψ s : Solute potential (-ve):

When sugar is added to a beaker, the solute potential or energy drops as water molecules ‘bond’ to the sugar. Thus to decrease in leaf relative to the root, sugars or other molecules accumulate in the leaf dropping it potential -1 to -2 MPa.

2. Ψ p : Pressure/turgor potential (+ve or -ve):

As water is transpired from the leaves it creates a negative pressure or tension. Imagine sucking on a straw rapidly down to the ‘last drop’…The solution ‘hangs’ in the straw due to this negative pressure. This pressure, generally, is on the order of less than -2 MPa (Mega Pascals).

Pressure can be positive, however, as with guttation, when there are so many solutes in a root that water accumulates and pushes up. Ions continue to be pumped into the xylem even though transpiration has ceased at night. Increased concentration results in a lower osmotic potential in the xylem and a gradient is developed across the root. Water moves into the xylem in response to the gradient.

3. Ψ m : Matric potential (-ve):

As water adheres to cell walls it lowers it potential. The walls of xylem are made up of carbohydrates which attract water molecules. In a sense, matric potential is equivalent to solute, but occurs when the molecules are bound rather than in solution.

4. Ψ g : Potential due to gravity:

This force in not critical at a cellular level but may be important in tall trees.

Plant-water potential increases with added pressure (turgor) and decreases with increase in osmotic pressure. In the past, the condition of water in plants used to be expressed in terms of its diffusion pressure deficit (DPD) or equivalent term such as suction force.

DPD = TP + IP + OP

where, DPD = diffusion pressure deficit (atm or bars)

TP = turgor pressure

IP = imbibitional pressure

OP = osmotic or solute pressure.

Values of OP are considered to be always positive, values of TP and IP are also considered positive and DPD of pure water at the reference is taken as zero: thus DPD values in plant systems are always positive and water will tend to move from a point of low DPD to one of high DPD.

Turgor pressure potential = + 10 bars

Imbibitional potential = – 1 bar

Solute potential = – 18 bars

Total water potential = – 9 bars

If the cells are placed in pure water ( ψ = 0), water will move into the cells (high to low potential). Similarly, water moves from cell where ψ = – 9 bars to one where ψ = -12 bars. The magnitude of water potentials in SPAC is given in Table 5.1.

In any system, if the condition of water is considered in terms of its energy state (potential), it is relatively easy to predict its direction of movement or its effect on some process. Water potentials are normally expressed in terms of energy units per unit mass or per unit volume. Typical units are joules kg -1 , ergs g -1 , ergs cm -3 or ergs mole -1 . Water potentials in soils and plants are now expressed in pressure units of atmospheres or bars.

Essay # 4. Measurement of Plant-Water Potential:

Several methods are available for measuring plant-water potential:

1. Pressure Chamber

2. Psychrometer

3. Dew Point Hygrometer

4. Osmometer

5. Leaf Temperature Measurement

6. Canopy Temperature Measurement

7. Canopy Air Temperature Differentials

8. Diffusive Resistance

9. Transpiration Rate Measurement, etc.

Commonly used plant-water stress indicators are plant-water potential and relative water content.

Plant-water stress can be measured using any of the above methods. Only two methods of measuring plant-water potential, pressure chamber and psychrometer methods are discussed.

1. Pressure Chamber :

Pressure chamber measures the tension on the water within the water conducting tissue (xylem). This method involves cutting a leaf and its attached petiole from the plant, protecting it from any water loss and sealing the leaf inside a pressurisation chamber with a small amount of the cut end of the petiole exposed outside. Pressure within the chamber is increased, until water is observed at the cut end of the petiole (Fig 5.2).

Tension within the xylem is believed to be equivalent to the pressure in the chamber at the first appearance of water and is further believed to be a measure of the physiological “dryness” of the plant, called the plant-water potential.

The units of water potential are negative pressures, with the most commonly used unit being the bar, which is equivalent to about 14.5 pounds per square inch (psi). In the scientific literature, the Megapascal (MPa) unit, which is simply 10 bars, is preferred.

2. Psychrometer :

Psychrometers (Fig 5.3) measure the water vapor pressure of a solution or plant sample, on the basis of the principle that evaporation of water from a surface cools the surface.

Measurement is by placing a piece of tissue sealed inside a small chamber that contains a temperature sensor (thermocouple) in contact with a small droplet of a standard solution of known solute concentration (known Ψ s and thus known Ψ w ).

If the tissue has a lower water potential than that of the droplet, water evaporates from the droplet, diffuses through the air and is absorbed by the tissue. This slight evaporation of water cools the drop. The larger the difference in water potential between the tissue and the droplet, the higher the rate of water transfer and hence the cooler the droplet.

If the standard solution has a lower water potential than that of the sample to be measured, water will diffuse from the tissue to the droplet, causing warming of the droplet. Measuring the change in temperature of the droplet for several solutions of known Ψ w makes it possible to calculate the water potential of a solution for which the net movement of water between the droplet and the tissue would be zero, signifying that the droplet and the tissue have the same water potential (Fig 5.4).

Cryoscopic osmometer (Ψ s measurement) and pressure probe (Ψ p measurement) are also available for measuring plant-water potential.

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• How to Measure Evapotranspiration ? | Plant-Water Relationships | Agronomy
• Effects of Water Deficits on Plant Growth | Essay | Plants | Agronomy

Agronomy , Essay , Plant-Water Relationships , Water Potential in Plants

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Water Conservation Essay

500+ words essay on water conservation.

Water makes up 70% of the earth as well as the human body. There are millions of marine species present in today’s world that reside in water. Similarly, humankind also depends on water. All the major industries require water in some form or the other. However, this precious resource is depleting day by day. The majority of the reasons behind it are man-made only. Thus, the need for water conservation is more than ever now. Through this water conservation essay, you will realize how important it is to conserve water and how scarce it has become.

Water Scarcity- A Dangerous Issue

Out of all the water available, only three per cent is freshwater. Therefore, it is essential to use this water wisely and carefully. However, we have been doing the opposite of this till now.

Every day, we keep exploiting water for a variety of purposes. In addition to that, we also keep polluting it day in and day out. The effluents from industries and sewage discharges are dispersed into our water bodies directly.

Moreover, there are little or no facilities left for storing rainwater. Thus, floods have become a common phenomenon. Similarly, there is careless use of fertile soil from riverbeds. It results in flooding as well.

Therefore, you see how humans play a big role in water scarcity. Living in concrete jungles have anyway diminished the green cover. On top of that, we keep on cutting down forests that are a great source of conserving water.

Nowadays, a lot of countries even lack access to clean water. Therefore, water scarcity is a real thing. We must deal with it right away to change the world for our future generations. Water conservation essay will teach you how.

Get the huge list of more than 500 Essay Topics and Ideas

Water Conservation Essay – Conserving Water

Life without water is not possible. We need it for many things including cleaning, cooking, using the washroom, and more. Moreover, we need clean water to lead a healthy life.

We can take many steps to conserve water on a national level as well as an individual level. Firstly, our governments must implement efficient strategies to conserve water. The scientific community must work on advanced agricultural reforms to save water.

Similarly, proper planning of cities and promotion of water conservation through advertisements must be done. On an individual level, we can start by opting for buckets instead of showers or tubs.

Also, we must not use too much electricity. We must start planting more trees and plants. Rainwater harvesting must be made compulsory so we can benefit from the rain as well.

Further, we can also save water by turning off the tap when we brush our teeth or wash our utensils. Use a washing machine when it is fully loaded. Do not waste the water when you wash vegetables or fruit, instead, use it to water plants.

All in all, we must identify water scarcity as a real issue as it is very dangerous. Further, after identifying it, we must make sure to take steps to conserve it. There are many things that we can do on a national level as well as an individual level. So, we must come together now and conserve water.

FAQ of Water Conservation Essay

Question 1: Why has water become scarce?

Answer 1: Water has become scarce due to a lot of reasons most of which are human-made. We exploit water on a daily basis. Industries keep discharging their waste directly into water bodies. Further, sewage keeps polluting the water as well.

Question 2: How can we conserve water?

Answer 2: The government must plan cities properly so our water bodies stay clean. Similarly, water conservation must be promoted through advertisements. On an individual level, we can start by fixing all our leaky taps. Further, we must avoid showers and use buckets instead to save more water.

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Garden: Know how and when to water plants this summer

So far this spring, rainfall has been fairly reliable and adequate and air temperatures have been moderate, eliminating the need for frequent watering of most outdoor plants in Greater Columbus.

Most gardens will, however, need to be irrigated more frequently at some point this summer when air temperatures heat up and rainfall becomes more spotty or even nonexistent for a period of time.

Understanding how and when to provide water to the plants in your care is critical tomaintaining plant health and growth.

How much water is needed?

Most plants growing in the ground need a minimum of 1 inch of water each week to thrive in the warm temperatures of summer. This is true for most plants, including vegetables, flowers, turf, herbaceous perennials, shrubs and even trees.

If rainfall does not provide at least 1 inch of water to your plants each week, you will need to provide supplemental irrigation.

This is even more critical when air temperatures are warmer and plants are under heat stress. One inch of water is a minimum and some plants, such as tomatoes, need more than an inch of water per week in order to thrive and produce fruit.

Many vegetable plants will require more water when they are in the flowering and fruit production phase of development.

If you don’t already have one, a rain gauge is a great tool to help you determine if last night’s rain shower was adequate or if you need to provide supplemental irrigation.

Garden: Companion planting has many benefits in the garden

Rainfall amounts vary widely in a geographic region, especially in summer, and a rain gauge will help you keep track of the amount of rainfall that actually falls on your plants.

Container plants need special care

Vegetables, herbs and annual flowers planted in containers will need more water more frequently, particularly pots smaller than 10 inches in diameter. Containers in full sun will dry out more quickly than those in locations which receive some shade, such as porches.

Unglazed clay pots tend to dry out more quickly than containers made of other materials. Raised beds are like large containers, and if your raised beds are less than 18 inches deep, plants growing in these beds will likely need to be watered more frequently than plants growing in the ground.

Water the soil, not the plants

If you water with a hose or watering can, be sure to direct the water directly to the soil, and not on the foliage of the plants. Watering the soil is the most effective and efficient method to provide moisture to a plant.

Water on foliage evaporates and can even burn foliage on some plants when sun hits the water droplets. Except on turf, avoid the use of overhead sprinklers as they provideperfect conditions for foliar diseases to develop, especially in susceptible vegetable andherbaceous perennial plants.

A long-handled watering wand is a good investment as it allows you to more easily direct the flow of the water to the soil surface and regulate the flow.

Using a soaker hose with its many small holes which deliver water slowly over time to the root zone of your plants is a very effective method for watering both in-ground plantings and raised beds. And the best part of using a soaker hose is that you don’t have to stand out in the hot sun while you are watering your plants!

A drip or trickle irrigation system is also a very efficient method for watering plants, particularly vegetable crops. Plants watered with drip irrigation systems yield better and have fewer diseases than plants irrigated by other methods.

Less water will be needed when using a drip irrigation system since water is supplied directly to the root zone where the plant needs it. You can even supply fertilizer through a drip irrigation system.

Drip irrigation systems are easy to set up and the necessary parts can be purchased at some local garden centers and through many sources online. A complete guide to building and operating a home garden irrigation system can be found here: go.osu.edu/homegardenirrigationsystem .

Garden: Some tomato tips and tricks for gardeners

Conserving water

One of the most effective strategies for conserving water when irrigating plants is the use of mulches. Whether you use black-plastic mulch or landscape fabric in the vegetable garden, or compost or shredded-hardwood mulches in your flower beds , plants grown in soil with a 3-inch layer of mulch will require less frequent irrigation.

The use of water from rain barrels connected to down spouts of a structure can provide an inexpensive source of supplemental water, especially for nonedible food crops, such as flowers, shrubs and trees.

When using rain-barrel water to water food crops, consider disinfecting the water in the rain barrel with a food grade sanitizer before applying to food crops. And always water the soil, and not the edible parts of the plant.

Mike Hogan is Extension Educator, Agriculture and Natural Resources and associate professor with Ohio State University Extension.

[email protected]

This article originally appeared on The Columbus Dispatch: Garden: Knowing how and when to water gardens this summer

Just us plants talking

Suddenly plant sentience, or awareness, and the possibility of plant intelligence, and even legal rights for plants, are hotly debated concerns..

My aspidistra was giving me shade about the cheesy plant food I’d been buying from CVS. “I don’t see you feeding yourself with that bottom-tier mac-n-cheese they sell at the drugstore,” it said.

And I replied: Just shut up, OK? I’m trying to write a column.

Chattering with plants used to be the sole province of my hero Prince Charles, now King Charles III of England. “I just come and talk to the plants, really,” he has said. “Very important to talk to them, they respond. … I happily talk to plants and trees and listen to them. I think it’s absolutely crucial.”

But suddenly plant sentience, or awareness, and the possibility of plant intelligence, and even legal rights for plants, are hotly debated concerns. A scientist quoted in an excerpt from Zoë Schlanger’s new book , “ The Light Eaters: How the Unseen World of Plant Intelligence Offers a New Understanding of Life on Earth ,” says of plants: “They process. They make decisions. And they perform. … This, to me, is the basic definition of intelligence .”

In their recently published article, “ Plant Sentience: Between Romanticism and Denial ,” Spanish researchers Miguel Segundo-Ortin and Paco Calvo argue that plants must be sentient because the alternative would be “an evolutionary dead-end.” “Current empirical findings,” they write, “strongly suggest that plants can perform many putatively cognitive abilities once thought to be unique to animals.”

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Among many classic examples would be some plants’ ( corn , tomatoes ) ability to summon defenders such as parasitic wasps to attack voracious caterpillars. Just because plants don’t possess a brain that we can currently detect doesn’t mean they don’t do smart things.

In a case wending its way through the Minnesota courts, wild rice, a co plaintiff with entities of the Chippewa Tribe, has sued the state’s Department of Natural Resources for, among other things, “the right to a healthy climate system and a natural environment free from human-caused global warming impacts and emissions.”

The suit, according to an article on the Hennepin County Bar Association’s website, “is part of the growing Rights of Nature movement, which seeks to recognize nature, natural entities, and ecosystems with rights aside from their existence as property.”

Who’s going to represent the rice? Attorney Clematis Finch? Clarence Furrow? These ideas of plant attributes and rights seem far-fetched, but in my lifetime similarly kooky claims were made for animals, and no one finds the claims outlandish now. Concerns over animal sentience — specifically their experience of pain — prompted a six-year hiatus in Ringling Bros. and Barnum & Bailey Circus performances to allow them to eliminate their much-criticized “wild” animal acts.

A 2011 lawsuit against SeaWorld, alleging that its performing killer whales were subjects of involuntary servitude, was partly responsible for the company’s decision to eventually phase out orca acts at its Orlando and San Diego facilities.

The number of non-meat eaters, vegans, and vegetarians in the United States has doubled in the past decade. While there is plenty of evidence that eating less meat has significant health benefits, that statistic is partly driven by ethical concerns over the treatment of animals.

I’ve become a vegetarian, thus courting the disdain of another hero of mine, the great writer George Orwell. He derided vegetarians as “ food cranks,” “a person willing to cut himself off from human society in hopes of adding five years on to the life of his carcase; that is, a person out of touch with common humanity.”

“Am I a food crank?” I asked my faithful house plant, now proving to be something of a finicky eater.

“No, just a normal crank,” the aspidistra assured me. “Now 86 this garbage from the drug store and get me something decent to eat.”

Alex Beam’s column appears regularly in the Globe. Follow him on Twitter @imalexbeamyrnot .

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What is renewable energy?

Renewable energy is energy derived from natural sources that are replenished at a higher rate than they are consumed. Sunlight and wind, for example, are such sources that are constantly being replenished. Renewable energy sources are plentiful and all around us.

Fossil fuels - coal, oil and gas - on the other hand, are non-renewable resources that take hundreds of millions of years to form. Fossil fuels, when burned to produce energy, cause harmful greenhouse gas emissions, such as carbon dioxide.

Generating renewable energy creates far lower emissions than burning fossil fuels. Transitioning from fossil fuels, which currently account for the lion’s share of emissions, to renewable energy is key to addressing the climate crisis.

Renewables are now cheaper in most countries, and generate three times more jobs than fossil fuels.

Here are a few common sources of renewable energy:

SOLAR ENERGY

Solar energy is the most abundant of all energy resources and can even be harnessed in cloudy weather. The rate at which solar energy is intercepted by the Earth is about 10,000 times greater than the rate at which humankind consumes energy.

Solar technologies can deliver heat, cooling, natural lighting, electricity, and fuels for a host of applications. Solar technologies convert sunlight into electrical energy either through photovoltaic panels or through mirrors that concentrate solar radiation.

Although not all countries are equally endowed with solar energy, a significant contribution to the energy mix from direct solar energy is possible for every country.

The cost of manufacturing solar panels has plummeted dramatically in the last decade, making them not only affordable but often the cheapest form of electricity. Solar panels have a lifespan of roughly 30 years , and come in variety of shades depending on the type of material used in manufacturing.

WIND ENERGY

Wind energy harnesses the kinetic energy of moving air by using large wind turbines located on land (onshore) or in sea- or freshwater (offshore). Wind energy has been used for millennia, but onshore and offshore wind energy technologies have evolved over the last few years to maximize the electricity produced - with taller turbines and larger rotor diameters.

Though average wind speeds vary considerably by location, the world’s technical potential for wind energy exceeds global electricity production, and ample potential exists in most regions of the world to enable significant wind energy deployment.

Many parts of the world have strong wind speeds, but the best locations for generating wind power are sometimes remote ones. Offshore wind power offers t remendous potential .

GEOTHERMAL ENERGY

Geothermal energy utilizes the accessible thermal energy from the Earth’s interior. Heat is extracted from geothermal reservoirs using wells or other means.

Reservoirs that are naturally sufficiently hot and permeable are called hydrothermal reservoirs, whereas reservoirs that are sufficiently hot but that are improved with hydraulic stimulation are called enhanced geothermal systems.

Once at the surface, fluids of various temperatures can be used to generate electricity. The technology for electricity generation from hydrothermal reservoirs is mature and reliable, and has been operating for more than 100 years .

Hydropower harnesses the energy of water moving from higher to lower elevations. It can be generated from reservoirs and rivers. Reservoir hydropower plants rely on stored water in a reservoir, while run-of-river hydropower plants harness energy from the available flow of the river.

Hydropower reservoirs often have multiple uses - providing drinking water, water for irrigation, flood and drought control, navigation services, as well as energy supply.

Hydropower currently is the largest source of renewable energy in the electricity sector. It relies on generally stable rainfall patterns, and can be negatively impacted by climate-induced droughts or changes to ecosystems which impact rainfall patterns.

The infrastructure needed to create hydropower can also impact on ecosystems in adverse ways. For this reason, many consider small-scale hydro a more environmentally-friendly option , and especially suitable for communities in remote locations.

OCEAN ENERGY

Ocean energy derives from technologies that use the kinetic and thermal energy of seawater - waves or currents for instance -  to produce electricity or heat.

Ocean energy systems are still at an early stage of development, with a number of prototype wave and tidal current devices being explored. The theoretical potential for ocean energy easily exceeds present human energy requirements.

Bioenergy is produced from a variety of organic materials, called biomass, such as wood, charcoal, dung and other manures for heat and power production, and agricultural crops for liquid biofuels. Most biomass is used in rural areas for cooking, lighting and space heating, generally by poorer populations in developing countries.

Modern biomass systems include dedicated crops or trees, residues from agriculture and forestry, and various organic waste streams.

Energy created by burning biomass creates greenhouse gas emissions, but at lower levels than burning fossil fuels like coal, oil or gas. However, bioenergy should only be used in limited applications, given potential negative environmental impacts related to large-scale increases in forest and bioenergy plantations, and resulting deforestation and land-use change.

For more information on renewable sources of energy, please check out the following websites:

International Renewable Energy Agency | Renewables

International Energy Agency | Renewables

Intergovernmental Panel on Climate Change | Renewable Sources of Energy

UN Environment Programme | Roadmap to a Carbon-Free Future

Sustainable Energy for All | Renewable Energy

Renewable energy – powering a safer future

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How to Propagate a Snake Plant So You Can Share It with Friends

Multiply snake plants with one of these simple methods and gift ultra-easy-to-grow plant babies to friends.

Megan Hughes has a passion for plants that drives her to stay on top of the latest garden advancements and time-tested ways of growing great plants. She travels regularly to learn about new plants and technology and is closely connected to the innovation side of the horticulture industry. She has more than 25 years of experience in horticulture.

Snake plants are among the easiest houseplants to grow . Learning how to propagate a snake plant is simple and allows you to add new plants to your collection at no cost or share them with others. The sword-like leaves of this tropical houseplant root easily in water or soil, and division is a great option for large plants.

All you need to multiply your snake plant is time, a sharp knife or pair of pruners, potting soil , and water. A few simple tips will ensure the young plants thrive, providing plenty of new plants to add to your indoor jungle , or you can share with friends. Rooting new snake plants takes a couple of months, but the wait is worth it, especially when you start seeing new shoots appearing.

BHG / Juli Lopez-Castillo

Know what you're going to get .

Unique foliage patterns , such as mottled leaves or gold leaf margins, are usually lost when a snake plant is multiplied by cuttings. A variegated leaf cutting will root, and new shoots (or pups) that emerge are generally solid green. A solid green snake plant makes a great houseplant, but you should know that a cutting won't produce a replica of the parent plant. Division is how to propagate a snake plant that looks exactly like the parent plant. Dividing your snake plant will give you new plants with the same leaf coloring as the original plant.

1. Divide a snake plant.

Division involves breaking the plant into sections and is the best way to propagate snake plants that have grown very big. Begin by removing the entire snake plant, roots and all, from its pot. Use a sharp knife or pruner to cut the tightly tangled root ball apart. Aim to create divisions with at least three leaves and accompanying roots.

Plant each division in moist potting mix in a container with drainage holes . Water the divisions well, allowing them to drain thoroughly. Place the newly potted plants in bright but indirect light. Water when soil is dry to the touch.

2. Root cuttings in water .

Rooting snake plant cuttings is as easy as placing a leaf into a jar of clean water . Begin by cutting a mature-sized leaf off an established plant. Place the cut end of the leaf in a jar or vase filled with a couple of inches of water. Put the jar in a bright spot and refresh the water, rinsing out the jar once a week. Roots should form at the base of the cutting in about two months. After roots form, plant the rooted cutting in a container filled with houseplant potting mix.

3. Start cuttings in soil .

Snake plant cuttings will root in moist potting mix, too. First, remove a leaf from an established plant, cutting the leaf at the base of the plant with pruners or a knife. You can maximize the number of new plants by cutting the leaf horizontally into 2-inch pieces. Make angled cuts or notch the leaf pieces to help you remember which end is the "bottom" and which is the "top."

Dip the bottom end of each leaf cutting in rooting hormone to encourage rooting and prevent rot. Place the cutting about a half-inch deep in moist potting mix in a shallow container with drainage holes. Once your cuttings are planted (cut side down), check the soil regularly to ensure it's moist. Be sure to empty any excess water that drains out of the container after watering to prevent root rot. After about two months, try to gently lift the cutting out of the soil. If you feel resistance, the cutting is rooted and established in its new pot. If the cutting pops out of the soil, replant it, and continue to water when it's dry.

Frequently Asked Questions

Propagating snake plants in water is, perhaps, easier because you only need snake plant cuttings, a jar of water, and sunlight to begin. However, this method comes with a slightly higher risk of rot. To avoid developing the dreaded rot, keep your cutting in a sunny spot and change the water regularly (we recommend once a week) for at least two months.

Snake plant cuttings take one to four months to develop new roots (and even longer before new leaf growth develops). If you want to propagate a snake plant faster, divide it instead of propagating from cuttings. (Propagation via division will also allow you to keep any variegated coloring your plant may have.) 

You can propagate snake plant cuttings any time of year so long as you provide them with bright light (but keep them out of direct sunlight) as they grow. House them where temperatures remain above 45°F (ideally between 65°F and 80°F) for best results.

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