PHOTOSYNTHESIS AND NITROGEN UTILIZATION IN LEAVES OF CINNAMOMUM BURMANNI GROWN UNDER ELEVATED ATMOSPHERIC NH3 CONCENTRATIONS AND SUPPLIED WITH DIFFERENT FORMS OF SOIL N

Abstract

We investigated the effects of different forms of soil nitrogen additions (NO - 3-N, NH + 4-N or NH 4NO 3-N) and exposure to elevated atmospheric NH 3 concentrations on photosynthesis, nitrogen utilization and nitrogen allocation in photosynthetic components in leaves of Cinnamomum burmanni. The results showed that maximum rates of carboxylation (V cmax) and maximum rates of potential electron transport (J max) were achieved in plants grown with additions of NO - 3-N and under elevated atmospheric NH 3 concentrations compared to plants growing under ambient conditions. Both J max and V cmax declined in plants supplied with NH + 4-N or NH 4NO 3-N and grown under elevated atmospheric NH 3. Regardless of the different forms of nitrogen supply, leaf nitrogen content on an area basis (N a) significantly increased under elevated atmospheric NH 3 concentrations (p0.05). Thylakoid nitrogen (N T), Rubisco nitrogen (N R) and nitrogen associated with electron transport (N E) increased significantly in plants supplied with NO 3 --N and exposed to the elevated atmospheric NH 3 when compared to plants grown under ambient condition (p0.05); however, N a, N T, N R and N E all decreased in plants supplied with NH + 4-N or NH 4NO 3-N. These results suggest that increased atmospheric NH 3 promotes the utilization of nitrogen for the synthesis of photosynthetic components, but inhibits the partitioning of nitrogen to N T, N R, and N E in plants supplied with NH + 4-N or NH 4NO 3-N. The organic nitrogen content per unit dry mass increased in plants that were supplied with NO - 3-N or NH 4NO 3-N (but not NH + 4-N) when exposed to increased atmospheric concentrations of NH 3. The soluble protein nitrogen content also increased in plants grown with NO - 3-N additions but not in plants grown with additions of NH + 4-N. The results suggest that increased atmospheric NH 3 concentration enhances nitrogen absorption and utilization and promotes photosynthesis in plants supplied with NO - 3-N additions but inhibits photosynthesis and nitrogen in plants supplied with NH + 4-N or NH 4NO 3-N.