Abstract: Taking a broadleaf-Korean pine (Pinus koraiensis) forest in Changbai Mountains of Northeast China as the object, an in situ experiment was conducted in 2006-2008 to study the effects of simulated nitrogen deposition on the seasonal and annual dynamics of soil net nitrogen mineralization, including net ammonification and net nitrification, in humus layer (0-7 cm) and uppermost mineral layer (0-15 cm) in the forest. The applied nitrogen forms were (NH₄)₂SO₄, NH₄Cl, and KNO₃, and their application rates were 0, 22.5, and 45 kg N·hm^-2·a^-1. During the study period, the annual soil nitrogen mineralization flux in the forest was 1.2-19.8 kg N·hm^-2·a^-1. In the two soil layers, the net nitrogen mineralization flux was significantly higher in 2008 than in 2006 and 2007 (P<0.05). The soil net N mineralization rate was increased with nitrogen input, especially the input of (NH₄)₂SO₄ or NH₄Cl (P<0.05), but this promotion effect decreased with the extension of years. Nitrogen deposition, especially NH₄Cl, had more obvious promotion effect on the net ammonification and net mineralization rates in humus layer than in the uppermost mineral layer. The previous researches on the annual fluxes of net nitrogen mineralization in forest soils in global scale also showed that the soil net nitrogen mineralization rate was increased significantly with increasing atmospheric nitrogen deposition, and the variation of atmospheric nitrogen deposition accounted for 52% of the variation of soil net nitrogen mineralization rates across the forests. In this study, nitrogen deposition (x₁) and soil pH (x₂) could explain 70% of the variation of soil net nitrogen mineralization rate (y) (y=0.54x₁-18.38x₂-109.55,R²=0.70, P<0.0001). The previous researches only provided the annual temperature in research areas, not considered the influence of the accumulative temperature, which could be the causes of non-relationship between soil nitrogen mineralization and temperature. The future research should pay more attention to the observation of soil accumulative temperature in different regional forests.

Key words: Korean pine, decay of standing trees, moisture content of sapwood and heartwood, soil moisture content, gradient, elevation.