Water Absorption in Plants
Plants absorb nutrients (in the form of salts or ions) and water from the soil with the help of roots. The procedure by which plants take-up compounds from the soil is known as absorption. The root is an underground cylindrical part of a plant that grows vertically down in the soil and help in absorption.
Active absorption describes the absorption of water by roots with the help of adenosine triphosphate, generated by the root respiration: as the root cells actively participate in the procedure, it is called active absorption. Root pressure, guttation, and bleeding are the manifestation of active water absorption.
The evidence suggests that passive absorption represents the majority of the water taken in by plants. Active absorption is very important only in gradually taking place plants growing in the soil near field capacity.
Following factors affect the absorption of water by root:
1.Availability of Soil Water
- (a) Plant takes in capillary water, which exists in the soil. Absorption of water depends upon the quantity of capillary water present in the soil. Absorption boosts by the increasing amount of capillary water.
- (b) If water exists in a greater amount in the soil then such kind of soil is called “Water logged soil”. This soil is Physiologically dry and lacking oxygen. Because of this anaerobic respiration happens in roots, and alcohol is formed. Roots can be degenerate due to the form action of alcohol.
An increase in soil temperature level up to about 30 ° C favors water absorption. At greater temperature water absorption is decreased. At low-temperature level likewise, water absorption reduced so much so that at about 0 ° C, it is practically reduced. This is probably since at low-temperature level:
- The viscosity of water and protoplasm is increased
- Permeability of cell membrane is decreased
- The metabolic activity of root cells are reduced
- Root development and elongation of roots are examined.
Water absorption likewise requires energy. This energy is released in the process of respiration. Oxygen is needed for respiration. This oxygen is provided by soil air. Absorption of water is slowed down in badly aerated soils because in such soils shortage of O2 and as a result the build-up of CO2 will retard the metabolic activities of roots like respiration.
This also inhibits the fast development and elongation of the roots so that they are deprived of a fresh supply of water in the soil. Waterlogged soils are poorly aerated and for this reason, are physiologically dry. They are bad for the absorption of water.
(a) The rate of absorption is inversely proportional to the concentration of minerals present in the soil.
Water Absorption x 1/Concentration of soil minerals
(b) Water absorption only occurs in proper soil solution. The soil ought to be hypotonic and, Plant needs to be hypertonic to perform the procedure of endosmosis. If the concentration of soil minerals is high, it decreases the rate of absorption, and plasmolysis and wilting occur.
5.Association of Mycorrhizae
Mycorrhizae is an association of fungi and roots of higher plants. Fungi increase the ability of absorption of water by roots.
According to Kramer, the rate of water absorption is directly proportional to the rate of transpiration. The rate of transpiration increases the rate of absorption of water by the root. Transpiration produces transpiration pull in the xylem vessels. It pulls water up. Thus, negative pressure is produced in the xylem of the root. It absorbs water from the soil.