Stomatal function and physiology

This chapter illustrates the function and physiology of stomata to clarify the role stomata plays in determining carbon assimilation. Stomata are small adjustable pores found in large numbers on the surface of most aerial parts of higher plants. Leaf gas exchange is controlled by the stomata. The diffusion rate of gases into or out of the leaf, or any other plant part, depends on the concentration gradient and the diffusive resistance of the pathway. The resistance of the stomatal pathway depends on the geometry of the pores as well as their frequency. Stomatal behavior directly modifies the CO2 assimilation rate and transpiration rate and consequently affects plant water and carbon status. The chapter also describes the effects of several environmental factors such as CO2, humidity, light and temperature on stomatal movements and the consequences for photosynthesis. A change in the concentration of CO2 leads to a change in the aperture of the stomata. The transpiration rate increases linearly with leaf-to-air vapor pressure difference (VPD) caused either by changes in air vapor pressure or by leaf temperature affecting the vapor pressure inside the leaf. A change in light intensity may simultaneously change photosynthetic rate and leaf temperature that modifies transpiration rate and leaf water status. Finally, the chapter illustrates several examples of modern techniques for studying stomatal physiology.