12.4.1 Factors Affecting the Rate of Transpiration
The rate of transpiration depends on some environmental factors; such as temperature, wind, humidity, light, atmospheric pressure etc.
(i) Temperature and wind
The temperature greatly affects the rate of transpiration. When the temperature is high, rate of evaporation increases, the water molecules move rapidly than at low temperatures and also because warm air can hold more water vapours than the cold air. So, on a warm day the rate of transpiration increases. Windy condition also increase the rate of transpiration as wind removes water vapours from leaf and keep the concentration difference high between the leaf and surrounding air .
In nearly dry condition or low humidity, the air around the plant will be dry; it will have low concentration of water than that inside the leaves. This difference in the concentration of water would result in an increase in the rate of transpiration. When there is more humidity in air, transpiration would be considerably low; as the air is already saturated with water will diffuse out of the leaves.
Light is an important factor in controlling the rate of transpiration as it greatly influences opening and closing of stomata of leaves. During day-light, the stomata remain open and allow the water vapours from the leaves to diffuse out into the atmosphere. At night or during hours of darkness, the stomata usually close, and the rate of transpiration is greatly reduced or it may even stop completely.
(iv) Atmospheric pressure
The atmospheric pressure also affects the rate of transpiration. Reduction in the atmospheric pressure enhances the rate of transpiration.
Category: 9th 10th