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

Photosynthetic nitrogen-use efficiency (PNUE, photosynthetic capacity per u nit leaf nitrogen) varies among species from different habitats and correla tes 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 CO2 concentration in saturate d light, nitrogen concentration, and the concentration of ribulose-1,5-bisp hosphate carboxylase (RuBPCase), a key enzyme of photosynthesis and the lar gest sink of nitrogen in leaves. Each species showed a strong correlation b etween photosynthetic capacity and RuBPCase concentration, and between RuBP Case concentration and nitrogen concentration. Photosynthetic capacity of l eaves decreased with increasing leaf life span, whereas PNUE did not correl ate significantly with leaf life span. There was a two-fold variation in PN UE among species. This relatively small variation in PNUE is consistent wit h the argument that species that coexist in a single habitat maintain a sim ilar 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.