“…Third, there may be a substantial contribution of diffusion resistances in the intercellular airspaces, especially in the case of a partly cutinized substomatal chamber (Roth-Nebelsick, 2007;Feild et al, 2011). Fourth, leaf surface features such as hairs or papillae surrounding the stomata, or encryption of stomata, may affect the diffusion through stomata, and especially will influence the boundary layer, which in addition to stomatal conductance determines overall diffusional conductance and therefore gas exchange (Kenzo et al, 2008;Hassiotou et al, 2009;Maricle et al, 2009). Clearly, much more research is needed to establish models that include all the factors that determine the anatomical influence of stomata on gas exchange rates and to validate these against a wide diversity of plants, yet the anatomical maximum defined as in Equations 1 and 2 is a strong constraint: g max correlates across diverse species with g op and lightsaturated photosynthetic rate (McElwain et al, 2016), and scales up, in combination with leaf area allocation, to the determination of ecosystem net primary productivity (Wang et al, 2015a).…”