Describe why and how transpiration rate is affected under low temperature humidity and moderate wind speed
Transpiration is the process by which water is lost from a plant through its leaves. It occurs primarily through small pores called stomata, which are found on the surface of leaves. Several factors, including temperature, humidity, and wind speed, can affect the transpiration rate.
Under low temperatures, transpiration rate is generally reduced. This is because the rate of water evaporation is slower at lower temperatures. The decrease in transpiration rate is beneficial for the plant as it helps to conserve water, especially in environments where water availability may be limited. Additionally, low temperatures can cause the stomata to close partially or completely, reducing the surface area through which water can be lost, further decreasing transpiration.
Low humidity also affects transpiration rate. When the air is dry, the water potential gradient between the plant's leaves and the atmosphere is higher, leading to increased rates of water loss. In such conditions, the plant needs to transpire more to maintain its water balance. As a result, transpiration rates tend to be higher under low humidity conditions.
Moderate wind speed, on the other hand, can increase transpiration rate. When there is wind, it helps to remove the water vapor that accumulates around the stomata, increasing the water potential gradient and facilitating transpiration. As a result, plants growing in windy environments often have higher transpiration rates compared to those growing in still air.
Furthermore, wind can also cause physical disruption to the boundary layer of air surrounding the leaves, which can accelerate the evaporation of water from the leaf surface. This effect is known as boundary layer disruption, and it further enhances transpiration under windy conditions.
In summary, low temperature reduces the transpiration rate due to slower water evaporation and partial or complete closure of stomata. Low humidity increases the transpiration rate as the water potential gradient between the leaves and the atmosphere is higher. Moderate wind speed enhances transpiration by removing water vapor around the stomata and disrupting the boundary layer, leading to faster water evaporation from the leaf surface.