How does wind speed affect the transpiration rate?

Wind speed increases the transpiration rate as it reduces the layer of moisture around the stomata, promoting more water loss.

Transpiration is the process by which water is carried through plants from roots to small pores on the underside of leaves, where it changes to vapour and is released to the atmosphere. This process is significantly influenced by the wind speed. When the wind speed is high, it reduces the boundary layer of moisture that surrounds the stomata (small openings on the leaf surface). This boundary layer acts as a barrier to water loss, so when it is reduced, the rate of transpiration increases.

The boundary layer is a thin layer of still air adhering to the surface of the leaf. When the wind speed is low, this layer is relatively thick, and the water vapour gradient from the inside of the leaf to the outside environment is low, resulting in a lower transpiration rate. However, as the wind speed increases, it disrupts this boundary layer, making it thinner. This increases the water vapour gradient, leading to a higher rate of transpiration.

Moreover, wind can also cause a decrease in relative humidity around the leaf surface. Relative humidity is the amount of moisture in the air compared to the maximum amount the air could hold at that temperature. When the wind speed is high, it carries away the transpired water vapour from the leaf surface, reducing the relative humidity. As transpiration is a diffusion process, it occurs from a region of higher concentration (inside the leaf) to a region of lower concentration (outside the leaf). Therefore, a decrease in relative humidity due to high wind speed will increase the concentration gradient, thus increasing the transpiration rate.

In conclusion, wind speed plays a crucial role in regulating the transpiration rate. It affects the thickness of the boundary layer and the relative humidity around the leaf surface, both of which directly influence the rate of water loss from the plant.