How does humidity affect transpiration?
Transpiration rates decrease proportionally to the amount of humidity in the air. This is because water diffuses from areas of higher concentration to areas of lower concentration. Thus, when the air spaces between the mesophyll cells in a leaf are saturated with water vapor, and the air outside the leaf is likewise saturated, there is a shallow gradient. A shallow gradient results in a slower transpiration rate. Conversely, if the air outside the leaf is relatively dry, the gradient becomes steep and the rate of transpiration increases.
