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

摘要

The influence of leaf thickness on internal conductance for CO2 transfer from the substomatal cavity to the chloroplast stroma (gi), and on the carbon isotope ratio (delta13C) of leaf dry matter was investigated in 6 Japanese evergreen species. Theexperimental material was 2-3 yr old seedlings of Quercus glauca and Castanopsis sieboldii grown under bright and/or shaded conditions, and shoots of 4 other species collected from the sunny side of the crown of trees on the University of Tsukuba campus- Quercus phillyraeoides, Cinnamomum camphora, Ligustrum lucidum and Camellia japonica. gi was estimated based on the combined measurements of gas exchange and concurrent carbon isotope discrimination. Leaves with thicker mesophyll tended to have largerleaf 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). gi of these leaves was correlated positively with Smes but negatively with 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. delta13C was positively correlated with mesophyll thickness and leaf nitrogen content on an area basis. However, gi values did not correlate with delta13C. These results suggest that difference in delta13C among the species was not caused by the variation in gi, but mainly by thedifference in long-term photosynthetic capacity. Comparison of these 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 are discussed.