ABSTRACT
Transpiration is the vapor loss from living surfaces to the atmosphere. When a leaf of a well-watered plant is exposed to dry air and solar radiation, it starts to transpire through its stomatal pores. The rate of vapor transport from the leaf into the atmosphere El can be determined from the product of leaf vapor conductance glv and the vapor pressure difference between the leaf mesophyll and the adjacent atmosphere:
El ¼ glvðemv eavÞ ð1Þ
where emv and eav are the water vapor partial pressures in the mesophyll and at the leaf surface, respectively. As the mesophyll cells lose water, they experience an increase in solute concentration and a reduction in water potential. Since plants are continuous hydraulic systems, changes in leaf transpiration are transmitted to other plant tissues and to the soil and atmosphere boundaries. Physiological control of stomatal vapor diffusion and turbulent transport are the dominating processes controlling the intensity of canopy transpiration. They take place on distinctive spatial and temporal scales that must be integrated to facilitate a quantitative understanding of canopy transpiration.
