Question

Explain factors affecting water absorption.

Hint:

For a plant to "drink" water efficiently, it needs four things: 1) Water must be available, 2) The soil must be warm enough, 3) The roots need to breathe (oxygen), and 4) The leaves must be "sweating" (transpiring) to create a pull.

Answer 1

The rate of water absorption by plant roots is affected by several external and internal factors:

Available Soil Water: The primary source of water for plants is capillary water in the soil. If the soil has too little water (below the wilting point) or is waterlogged (displacing soil oxygen), absorption rates will be low.
Soil Temperature: The optimal temperature for water absorption is typically between 20°C and 30°C. Low temperatures decrease the permeability of the root cell membranes and increase the viscosity of water, slowing down absorption.
Soil Aeration: Root cells need oxygen for respiration to provide the energy needed for active transport of minerals, which in turn facilitates water absorption by osmosis. Poorly aerated or waterlogged soils lack sufficient oxygen, thus hindering water uptake.
Concentration of Soil Solution: If the soil solution is highly concentrated with salts (hypertonic), the water potential gradient between the soil and the root cells is reduced or even reversed, making it difficult for the roots to absorb water.
Rate of Transpiration: A high rate of transpiration creates a strong tension or "pull" on the water column in the xylem (transpirational pull). This is the main driving force for passive water absorption by the roots.