Effects of three years of simulated nitrogen deposition on soil nitrogen dynamics and greenhouse gas emissions in a Korean pine plantation of northeast China.

Continuously enhanced nitrogen (N) deposition alters the pattern of N and carbon (C) transformations, and thus influences greenhouse gas emissions. It is necessary to clarify the effect of N deposition on greenhouse gas emissions and soil N dynamics for an accurate assessment of C and N budgets under increasing N deposition. In this study, four simulated N deposition treatments (control [CK: no N addition], low-N [L: 20kgNha-1yr-1], medium-N [M: 40kgNha-1yr-1], and high-N [H: 80kgNha-1yr-1]) were operated from 2014. Carbon dioxide, methane and nitrous oxide fluxes were monitored semimonthly, as were soil variables such as temperature, moisture and the concentrations of total dissolved N (TDN), NO3-, NO2-, NH4+, and dissolved organic N (DON) in soil solutions. The simulated N deposition resulted in a significant increase in TDN, NO3- and DON concentrations in soil solutions. The average CO2 emission rate ranged from 222.6mgCO2m-2h-1 in CK to 233.7mgCO2m-2h-1 in the high-N treatment. Three years of simulated N deposition had no effect on soil CO2 emission, which was mainly controlled by soil temperature. The mean N2O emission rate during the whole 3years was 0.02mgN2Om-2h-1 for CK, which increased significantly to 0.05mgN2Om-2h-1 in the high-N treatment. The N2O emission rate positively correlated with NH4+ concentrations, and negatively correlated with soil moisture. The average CH4 flux during the whole 3years was -0.74μgCH4m-2h-1 in CK, which increased to 1.41μgCH4m-2h-1 in the low-N treatment. CH4 flux positively correlated with NO3- concentrations. These results indicate that short-term N deposition did not affect soil CO2 emissions, while CH4 and N2O emissions were sensitive to N deposition.