The influence of leaf thickness on the CO2 transfer conductance and leaf stable carbon isotope ratio for some evergreen tree species in Japanese warm-temperate forests

1. The influence of leaf thickness on internal conductance for CO2 transfer from substomatal cavity to chloroplast stroma (g(i)) and carbon isotope ra tio (delta(13)C) Of leaf dry matter was investigated for some evergreen tre e species from Japanese temperate forests. g(i) was estimated based on the combined measurements of gas exchange and concurrent carbon isotope discrim ination. 2 . Leaves with thicker mesophyll tended to have larger leaf dry mass per are a (LMA), larger surface area of mesophyll cells exposed to intercellular ai r spaces per unit leaf area (S-mes) and smaller volume ratio of intercellul ar spaces to the whole mesophyll (mesophyll porosity). 3. g(i) of these leaves was correlated positively to S-mes but negatively t o mesophyll porosity. The variation in g(i) among these species would be th erefore primarily determined by variation of the conductance in liquid phas e rather than that in gas phase. 4. delta(13)C was positively correlated to mesophyll thickness and leaf nit rogen content on an area basis. However, g(i) values did not correlate to d elta(13)C. These results suggest that difference in delta(13)C among the sp ecies was not caused by the variation in g(i), 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 g(i) differed depending on leaf fun ctional types (evergreen, deciduous or annual). Differences in leaf propert ies among these functional types were discussed.