Importance of leaf anatomy in determining mesophyll diffusion conductance to CO2 across species: quantitative limitations and scaling up by models

Foliage photosynthetic and structural traits were studied in 15 species with a wide range of foliage anatomies to gain insight into the importance of key anatomical traits in the limitation of diffusion of CO2 from substomatal cavities to chloroplasts. The relative importance of different anatomical traits in constraining CO2 diffusion was evaluated using a quantitative model. Mesophyll conductance (g(m)) was most strongly correlated with chloroplast exposed surface to leaf area ratio (S-c/S) and cell wall thickness (T-cw), but, depending on foliage structure, the overall importance of g(m) in constraining photosynthesis and the importance of different anatomical traits in the restriction of CO2 diffusion varied. In species with mesophytic leaves, membrane permeabilities and cytosol and stromal conductance dominated the variation in g(m). However, in species with sclerophytic leaves, g(m) was mostly limited by T-cw. These results demonstrate the major role of anatomy in constraining mesophyll diffusion conductance and, consequently, in determining the variability in photosynthetic capacity among species.