Transpiration - Water Movement through Plants

How fast does water move through plants? Transpiration rates depend on two major factors: 1) the driving force for water movement from the soil to the atmosphere and 2) the resistances to water movement in the plant.

Click here for a slide show describing ’Water potential in plants and how to measure it’. *NOTE: The PowerPoints may take several seconds to load.

Driving force: The driving force for transpiration is the difference in water potential between the soil and the atmosphere surrounding the plant. This difference creates a gradient, forcing water to move toward areas with less water. The drier the air around the plant, the greater the driving force is for water to move through the plant and the faster the transpiration rate. The following section, FACTORS AFFECTING RATES OF TRANSPIRATION, expands on how changes in the environment alter this driving force and thus transpiration.

Resistances: There are three major resistances to the movement of water out of a leaf: cuticle resistance, stomata resistance and boundary layer resistance. These resistances slow water movement. The greater any individual resistance is to water movement, the slower the transpiration rate. The following section, FACTORS AFFECTING RATES OF TRANSPIRATION, expands on how changes in the plant alter these resistances and thus transpiration.