What factors affect transpiration rate in plants?

Transpiration is the process where plants absorb water through the roots and then give off water vapor through pores in their leaves, called stomata. The transpiration rate is affected by several environmental factors:

• Temperature: As the temperature increases, water molecules gain kinetic energy and evaporate faster. This increases the rate of transpiration.
• Humidity: Humidity is the amount of water vapor in the air. If the air is very humid, the concentration gradient of water between the inside of the leaf (high) and the outside air (also high) is low. This slows down evaporation. Therefore, high humidity decreases the rate of transpiration.
• Wind / Air Movement: A layer of humid air, called a "boundary layer," can form around the leaf surface, slowing transpiration. Wind blows this boundary layer away, maintaining a steep concentration gradient. Therefore, increased wind increases the rate of transpiration. (Very high wind, however, may cause stomata to close, which would then decrease it).
• Light Intensity: Light is the primary signal that causes stomata to open. When stomata are open (to take in CO₂ for photosynthesis), they also release water vapor as a side effect. Therefore, higher light intensity generally increases the rate of transpiration.
• Soil Water Availability: This is an internal factor. If the soil is very dry, the plant cannot absorb enough water. It will enter a state of stress and actively close its stomata to conserve water, which decreases the rate of transpiration.