1. The influence of leaf thickness on internal conductance for CO2 transfer from substomatal cavity to chloroplast stroma (gi) and carbon isotope ratio (δ13C) of leaf dry matter was investigated for some evergreen tree species from Japanese temperate forests. gi was estimated based on the combined measurements of gas exchange and concurrent carbon isotope discrimination.
2. Leaves with thicker mesophyll tended to have larger leaf dry mass per area (LMA), larger surface area of mesophyll cells exposed to intercellular air spaces per unit leaf area (Smes) and smaller volume ratio of intercellular spaces to the whole mesophyll (mesophyll porosity).
3.gi of these leaves was correlated positively to Smes but negatively to mesophyll porosity. The variation in gi among these species would be therefore primarily determined by variation of the conductance in liquid phase rather than that in gas phase.
4.δ13C was positively correlated to mesophyll thickness and leaf nitrogen content on an area basis. However, gi values did not correlate to δ13C. These results suggest that difference in δ13C among the species was not caused by the variation in gi, but mainly by the difference in long-term photosynthetic capacity.
5. Comparison of our results with those of previous studies showed that the correlation between leaf thickness and gi differed depending on leaf functional types (evergreen, deciduous or annual). Differences in leaf properties among these functional types were discussed.