ABSTRACT
Nearly all water evaporated from vegetated surfaces to the atmosphere originates from leaves. Water is vaporized from cell walls inside leaves and diffuses from the leaf interior to the bulk atmosphere around plants. This process is called transpiration, and this section discusses the regulation of and methods to estimate transpiration rates. While transpiration involves basically the vaporization of water and the diffusion of the vapor into the bulk atmosphere, transpiration is complex because the water vapor must move from the leaf interior, through pores in the leaf epidermis called stomata, and finally into the atmosphere. Stomata are under active control so that transpiration rates are dynamic and rapidly respond to the environment. An understanding of the influence of stomata regulation on both carbon dioxide and water vapor flux density leads to various approaches to calculate plant canopy transpiration rates.
