
ALT Diagram of the mechanism of nonstomatal control of transpiration as VPD increases, generating unsaturation in the substomatal cavity. The parameters in the figure are atmospheric water vapor concentration (wa), water vapor concentration on the leaf surface (ws), substomatal cavity water vapor concentration (wi), water vapor concentration at saturation (wsat), resistance to water diffusion through the plasma membrane (rp), cell wall water potential (Ψw), and cytosolic water potential (Ψc). Black dots represent cell wall fibers. The current theory suggests that aquaporins acting as transmembrane conduits close when VPD rises, increasing the resistance to water movement through the membrane of mesophyll cells (rp) and triggering unsaturation in the substomatal cavity.




































