Factors Affecting the Rate of Transpiration in Plant are given below:
1. Humidity (Vapour Pressure):
The humidity of the atmosphere affects the rate of diffusion of water vapour from the stomata. Low humidity in the atmosphere increases the rate of transpiration. On the other hand high humidity in the air reduces the rate of outward diffusion of water from the sub-stomatal cavity and reduces the rate of transpiration because the air is already laden with the water vapour.
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2. Temperature:
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High temperature increases rate of transpiration by providing the latent heat of vaporization. Rise in temperature increases evaporation of water while low temperature reduces evaporation.
3. Intensity of Light:
Light affects the rate of transpiration indirectly. More transpiration occurs during the day. Stomata open during light and thus transpiration occurs more in the day. During the night they are closed, thus the rate of transpiration is minimal. Can you guess what happens on a cloudy day?
4. Air Movement (Velocity of Wind):
Moving air sweeps away the water vapour in the air outside the stomata. This speeds up diffusion of water vapour from stomata. Thus, the rate of transpiration increases with the velocity of wind.
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Some plants in dry conditions (xerophytes) have folded leaves or epidermal hairs which help to retain moist air around the stomata to prevent transpiration.
5. Atmospheric Pressure:
Decrease in atmospheric pressure increases diffusion of water vapour from stomata. The lower the atmospheric pressure, the greater is the rate of evaporation of water from leaves. Thus, rate of transpiration increases with the decrease in atmospheric pressure.
6. Carbon Dioxide Concentration:
If the concentration of carbon dioxide increases more than the normal (0.03%), the stomata get closed. This reduces the rate of transpiration.
7. Water Supply to the Leaf:
Shortage of water in the soil affects the water supply to the leaf and in turn the stomata close and the leaf wilts. This reduces the rate of transpiration.
8. Leaf Structure:
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The shape of the leaf and the number and position of stomata on it influence water vapour loss. In xerophytes, the cuticle is thick and there is negligible loss of water vapour (less transpiration). On the other hand in shady plants leaf with a large surface area and a thin cuticle, the loss of water vapour is more (more transpiration).