Effect of Leaf Water Deficit on Stomatal and Nonstomatal Regulation of Net Carbon Dioxide Assimilation

Abstract

The effect of leaf water deficit on net CO(2) assimilation was studiedunder two conditions: in one, the stomata were allowed to contributeto the regulation of CO(2) assimilation; in the other, air was forcedthrough the leaf at a constant rate to overcome the effects of changein stomatal resistance accompanying changes in leaf water deficit.When the stomata were allowed to regulate the gaseous diffusive resistanceof the leaf, CO(2) assimilation decreased with increasing leaf waterdeficit. However, when air was forced through the leaf, the rateof assimilation was not inhibited by increasing leaf water deficit.The results indicate that the inhibition of net CO(2) assimilationwith increasing leaf water deficit is a consequence of an increasein the diffusive resistance to gas exchange and not of a change inapparent mesophyll resistance.