COS 67-6
Effects of leaf nitrogen allocation on photosynthetic nitrogen-use efficiency of seedlings of three tropical species in Indonesia

Wednesday, August 13, 2014: 9:50 AM
Bataglieri, Sheraton Hotel
Min-Kyu Moon, Department of Forest Sciences, Seoul National University, Korea, Republic of (South)
Taekyu Kim, National Institute of Environmental Research, Incheon, Korea, Republic of (South)
Hyun Seok Kim, Department of Forest Sciences, Seoul National University, Korea, Republic of (South)
Background/Question/Methods

During last a few decades, the economics of nitrogen (N) use in plant have been the key issues in eco-physiology, because N is one of the most essential and limiting components of natural ecosystem. Thus the efficient use of this resources greatly affect growth, survival, competition and distribution of plant species. The photosynthetic N-use efficiency (PNUE; μmol CO2 [mol-1 N] s-1), which is defined as the amount of CO2 assimilation per unit N content, differs with various leaf traits such as leaf N content (NL), its allocation among different functional & structural components, intercellular and mesophyll CO2 concentration and enzyme kinetics. In this study, we 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, Swietenia macrophylla and Acacia mangium) in western Java, Indonesia. Especially, A. mangiumis the only N-fixing species among three species, which widely planted for reforestation and afforestation in Indonesia. We expected this species has distinctive characteristics on N use in photosynthetic processes with other two non N-fixing species.

Results/Conclusions

A. mangium, i.e., N-fixing species among three studied species, had greater NL than other two species, although the N fractions allocated to NP, namely, Rubisco (NR) and bioenergetics (NB), were greater in S. macrophylla. Across the three species, the maximum assimilation (Amax) and dark respiration rate (Rd) were increased with increasing NL, NR and NB. However, the variation of Amax was more explained by NR or NB than NL, while the variation of Rd was more explained by NL than NR or NB. PNUE exhibited a positive relationship with NP in all species. However, there were significant differences between two different groups, that is, PNUE of A. mangium, i.e., N-fixing species, was lower than those of M. montana and S. macrophylla, i.e., non N-fixing species, at a given NP. In addition, the intercellular CO2 concentration exhibited no correlation with PNUE across the three species, while stomatal conductance was positively correlated with PNUE. However, the slopes of the correlation were steeper in non N-fixing species than N-fixing species. These results imply that there may be different strategies in N use in N-fixing and non-N-fixing species.