Photosynthetic nitrogen-use efficiency in evergreen broad-leaved woody species coexisting in a warm-temperate forest

Photosynthetic nitrogen-use efficiency (PNUE, photosynthetic capacity per unit leaf nitrogen) varies among species from different habitats and correlates with several ecological characteristics such as leaf life span and leaf mass per area. We investigated eight evergreen broad-leaved woody species with different leaf life spans that coexist in a warm-temperate forest. We determined photosynthetic capacity at ambient CO(2) concentration in saturated light, nitrogen concentration, and the concentration of ribulose-1,5-bisphosphate carboxylase (RuBPCase), a key enzyme of photosynthesis and the largest sink of nitrogen in leaves. Each species showed a strong correlation between photosynthetic capacity and RuBPCase concentration, and between RuBPCase concentration and nitrogen concentration. Photosynthetic capacity of leaves decreased with increasing leaf life span, whereas PNUE did not correlate significantly with leaf life span. There was a twofold variation in PNUE among species. This relatively small variation in PNUE is consistent with the argument that species that coexist in a single habitat maintain a similar PNUE. The two components of PNUE-photosynthetic rate per unit RuBPCase and RuBPCase per unit leaf nitrogen-were not significantly correlated with other leaf characteristics such as leaf life span and leaf mass per area. We conclude that differences in PNUE are relatively small among coexisting species and that differences in absolute amounts of photosynthetic proteins lead to differences in photosynthetic productivity among species.