Absorption of Water by Plants and the Role of Water in Nutrient Absorption
Absorption of Water by Plants and the Role of Water in Nutrient Absorption: Moistures enter plant roots by the process of osmosis, which may be roughly defined as the movement of a liquid through a semi-permeable membrane caused by unequal concentrations on the two sides.
It is customary to think of the cell sap within the root as having a greater concentration of soluble material than the soil moisture, and hence water passes in to equalize the concentration.
A more correct view is to consider the concentration of water molecules in the cell sap reduced because of the number of soluble substances present, and hence the number of water molecules in the soil solution is greater.
As a result, more water molecules strike against a unit area of the exterior of the root membrane than against the interior, for the molecules in both cell sap and soil solution are in constant motion. As a result of the bombardment, water passes into the root from a zone of higher concentration of water to a zone of lower concentration.
If through any circumstance, the concentration of soluble substances in the soil moisture exceeds that of the cell sap, the situation will be reversed and water will pass out of the root.
It should be recalled to mind that plant roots do not absorb the soil solution as such, as animals drink water containing soluble material. The water enters the roots as pure water without regard to the intake of any of the materials dissolved in it. The entrance of dissolved substances is entirely a separate process.
The Role of Water in Nutrient Absorption
It is generally believed that material must be in solution to pass through the plant-root membrane. Nutrients in the soil solution should therefore be in suitable condition for absorption.
It must be pointed out, however, that the presence of a nutrient in the soil solution does not assure its use by the plant because of the passage of ions and molecules through the plant-root membrane.
Read Also: Availability of Water to the Soil-Plant System
