Seedling growth response of two tropical tree species to nitrogen deposition in southern China.

Seedling growth response of two tropical tree species ( Schima superba and Cryptocarya concinna) to simulated N deposition was studied during a period of 11 months. One-year-old seedlings were grown in forest soil treated with N as NH₄NO₃ at Control–no N addition, N5–5, N10–10, N15–15, and N30–30 g N m⁻² year⁻¹. The objective was to examine the effects of N addition on seedling growth and compare this effect between the two tropical tree species of different species-N-requirement. Results showed that both species responded significantly to N addition and exhibited positive effect to lower rate of N addition and negative effect to higher rate of N addition on growth parameters (height and stem base diameter, biomass production, and net photosynthetic rate). The highest values were observed in the N10 plots for S. superba and in the N15 plots for C. concinna, but the lowest values were observed in the N30 plots for both species. However, the reduction in the N30 plots was more pronounced for S. superba than for C. concinna relative to the control plots. Our findings suggest that response of seedling growth of tropical tree species to atmospheric N deposition may vary depending on rate of N deposition and species-N-requirement. [ABSTRACT FROM AUTHOR]