Effects of leaf nitrogen allocation on photosynthetic nitrogen-use efficiency of seedlings of three tropical species in Indonesia

Abstract

Leaf N content (NL) and its allocation, which shows a wide range of variation among species, are major factors that determine the photosynthetic characteristics and photosynthetic nitrogen use efficiency (PNUE) of tree species. In this study, I investigated the allocation of NL to a photosynthetic apparatus (NP) and its effects on the photosynthetic characteristics and PNUE of two-year-old pot-growing seedlings of three tropical tree species (Magnolia montana Blume, Swietenia macrophylla King, and Acacia mangium Willd), which were grown at an open nursery in western Java, Indonesia. A. mangium (i.e. the only N-fixing species among three studied species) had greater NL with higher capacities in photosynthetic characteristics, that is, light-saturated photosynthetic rate (Pmax) and dark respiration rate (Rd) than the other two species, although the N fractions allocated to NP, namely, Rubisco (NR) and bioenergetics (NB), were greater in S. macrophylla. In all species, PNUE exhibited a positive relationship with NP

however, the PNUE of N-fixing A. mangium was lower than those of non N-fixing M. montana and S. macrophylla at a given NP. In addition, stomatal conductance was also positively correlated with PNUE, but the slopes of the correlation were steeper in M. montana and S. macrophylla than A. mangium. These result was explained by the differences in leaf mass per unit area between A. mangium and other species. My research implies that there are different strategies in N use between A. mangium and other species.