How does humidity affect transpiration in leaves?

Transpiration is the process by which water vapor is lost from plant leaves to the atmosphere. This process primarily occurs through tiny openings called stomata. When the air surrounding a leaf is dry, it creates a greater concentration gradient between the moisture inside the leaf and the moisture in the air outside. As a result, water vapor diffuses out of the leaf more rapidly. Therefore, when humidity is low, the rate of transpiration increases because the air can hold more water vapor, encouraging more water to exit the leaves.

In contrast, if the humidity is higher, the concentration gradient diminishes, leading to a slower rate of water vapor diffusion from the leaf to the air. High humidity means that the air is already saturated with water vapor, which reduces the drive for water to leave the leaf. Thus, the statement that the drier the air around a leaf, the faster the rate of transpiration accurately describes the relationship between humidity and transpiration.