Sometimes you may observe that a potted plant kept in sunlight and provided with sufficient water does not grow. Its leaves look pale and weak. Plant may not even flower properly. Such a situation is an indication, that the plant may not be getting all that is required for normal growth and development. In most of such situations one or more minerals required may be lacking in the soil you might have seen farmers adding some extra manure (khad) to the soil. In this lesson you will learn the importance of mineral nutrition in plants.
After completing this lesson, you will be able to : define the terms mineral nutrition, macro and micro nutritients; explain the functions of minerals with reference to the techniques of hydroponics and aeroponics; list the role of macro and micro nutrients; mention the deficiency symptoms of macro and micro nutrients; differentiate between autotrophic and heterotrophic nutrition in plant; describe the saprophytic and parasitic modes of nutrition in plant.
WHAT IS PLANT NUTRITION
As you know that all living organisms require food to survive, grow and reproduce so every organism takes in food and utilizes the food constituents for its requirements of growth. A series of processes are involved in the synthesis of food by plants, breaking down the food into simpler substances and utilization of these simpler substances for life processes. Nutrition in plants may thus be defined as a process of synthesis of food, its breakdown and utilisation for various functions in the body. B
IOLOGY 213 MODULE – 2 Forms and Function of Plants and Animals Nutrition in Plants – Mineral Nutrition Notes The chemical substances in food are called nutrients e. g. CO2, water, minerals, carbohydrate, protein, fats etc. Green plants can make their own food from simple substances like water and carbon dioxide through the process of photosynthesis and are called autotrophs (auto : self; trophos : feeding). But the non-green plants and other organisms which cannot prepare their own food and obtain nutrition from green plants are called heterotrophs (heteros : different).
Now we will discuss how plant get the nutrients. You already know that carbohydrates are synthesised by the process of photosynthesis. What are the elements present in these carbohydrates? Carbon, hydrogen and oxygen are the main elements in carbohydrates, fats and proteins. In addition to these three elements, plants need a variety of elements for their survival. These are generally referred to as mineral elements. They are absorbed by the root system of plants in the form of their salts. The study of how plants get mineral elements and utilize them for their growth and development is called mineral nutrition. If the minerals are not available to plants, specific symptoms appear due to the deficiency of a particular element. There are methods to determine the requirement of minerals by plants. Some such method are given below.
METHODS TO DETERMINE THE REQUIREMENT OF MINERAL FOR PLANT
Minerals are absorbed by plants in solution form. So it is possible to grow plants in water containing the desired amount of mineral salts taking care that the aerial parts are exposed to air and light. This technique of growing plants in a nutrient solution in complete absence of soil is known as Hydroponics/water culture. It was demonstrated for the first time by a German Botanist Julius Von Sachs in the year 1980. In water culture experiments, seedlings are made to grow in water containing the known nutrients in a particular proportion.
Vigorous bubbling of the air is routinely done to provide sufficient oxygen to the root system. The culture solutions may contain all essential nutrients except the one whose importance is to be identified. Then the plant growing in it is compared to the one growing with all essential nutrient (control experiment). 214 BIOLOGY Nutrition in Plants – Mineral Nutrition MODULE – 2 Forms and Function of Plants and Animals Notes Fig. 9. 1 Experimental set up for nutrient solution culture of plants. Water culture experiments help us to understand :
- which element is essential for normal growth of the plant.
- which element is not essential and is absorbed along with other nutrients.
- how much quantity of each mineral is essential.
Hydroponics has been successfully employed for the commercial production of seedless cucumber, tomato and lettuce.
Aeroponics : Like hydroponics, aeroponics is another technique of growing plants in an air/mist environment without the use of soil. Aeroponics is a technique of growing plants with their roots supplied with moisture present in the air. Rooted plants are placed in a special type of box. The shoots of the rooted plants are exposed to air and the roots are inside the box having computer controlled humid atmosphere. The roots are sprayed/misted for short durations with a hydro atomized pure water/nutrient solution. This method has been developed recently. Since plants cultured by this technique get a very good growth of root hairs, it is very useful method for research purposes. Citrus plants and olives have been successful grown through aeroponics.