Photosynthetic nitrogen-use efficiency in leaves of woody and herbaceous species

1. Photosynthetic characteristics of an annual herb, Chenopodium album, and an evergreen tree, Quercus myrsinaefolia, were compared to clarify causes of the difference in photosynthetic nitrogen-use efficiency (photosynthetic capacity per unit nitrogen) between leaves of herbaceous and evergreen species. 2. When leaves with the same nitrogen content on an area basis were compared, photosynthetic capacity of C. album was twice as high as that of Q. myrsinaefolia. Gas-exchange measurements showed higher intercellular CO₂ concentration in C. album. Biochemical analyses indicated larger allocation of nitrogen into ribulose-1,5-bisphosphate carboxylase, a key enzyme of photosynthesis, and higher specific activity of ribulose-1,5-bisphosphate carboxylase in C. album. However, these differences were not large. 3. Compositional deviation of ¹³C in leaves of the two species suggested that the drop of CO₂ level between the intercellular space and the chloroplast was slightly largerin Q. myrsinaefolia when compared between the leaves with the same photosynthetic capacity. 4. It is concluded that the difference in photosynthetic nitrogen-use efficiency between C. album and Q. myrsinaefolia is not caused by a sole factor that is markedly different between the two species but by several factors each of which is slightly disadvantageous to Q. myrsinaefolia compared with C. album.