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.

ALT Figure from the article: Potentials for metabolomics and stable isotope ecology in a combined assessment of compound and position-specific stable isotope signatures.

ALT Air vapour pressure deficit responses of the ratio of intercellular to ambient CO2 mole fraction; the ratio of chloroplast surface to ambient CO2 mole fraction; and the ratio of chloroplast stroma to ambient CO2 mole fraction.

ALT Simplified scheme of C3 CO2 fixation (modified from Schuler et al. (2023)): light-dependent reactions according to Allen et al. (2011) and light-independent reactions according to Busch (2020).

ALT Potentials for metabolomics and stable isotope ecology in a combined assessment of compound and position-specific stable isotope signatures.