Nitrogen addition method affects growth and nitrogen accumulation in seedlings of four subtropical tree species: Schima superba Gardner & Champ., Pinus massoniana Lamb., Acacia mangium Willd., and Ormosia pinnata Lour

Key message N addition (56, 156, and 206 kg N ha −1 yr −1 as dissolved NH 4 NO 3 ) method (canopy vs soil) did not affect the biomass of N 2 -fixers ( Acacia mangium Willd. and Ormosia pinnata Lour.), but significantly affected the biomass of non-N 2 -fixers ( Schima superba Gardner & Champ., Pinus massoniana Lamb.). Coniferous species exposed to N addition on the canopy rather than the soil had higher N accumulation. Context Previous experiments simulating nitrogen (N) addition in forests were conducted by adding N fertilizer directly to soils, which neglects the fact that N uptake can be done by canopy leaves. Aims The objective of this study is to examine how different N addition methods (canopy vs soil) affect growth and N accumulation of four subtropical tree seedlings. Methods An open-air greenhouse experiment was conducted to expose four tree species ( Schima superba Gardner & Champ., Pinus massoniana Lamb., Acacia mangium Willd. and Ormosia pinnata Lour.) to different N addition methods (canopy or soil) and N levels (ambient, medium, or high). Results N addition method affected the biomass of non-N 2 -fixers ( Schima superba Gardner & Champ. and Pinus massoniana Lamb.), while N 2 -fixers ( Acacia mangium Willd. and Ormosia pinnata Lour.) were unaffected. N concentrations in the soils and leaves of all trees were significantly increased by the medium and high N additions, and soil N concentrations resulted from N addition via soil rather than the canopy. Although leaf N concentration was significantly affected by N addition method in all trees except for Ormosia pinnata , only N accumulation in Pinus massoniana was significantly affected by N addition method. Conclusion N addition method affected the biomass of non-N 2 -fixers and N accumulation in coniferous species, while it did not affect the biomass of N 2 -fixers and N accumulation in broadleaf species.