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

摘要

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: 20 kg N ha~(-1) yr~(-1)], medi-um-N [M: 40 kg N ha~(-1) yr~(-1)], and high-N [H: 80 kg N ha~(-1) yr~(-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), NO_3~-, NO_2~-, NH_4~+, and dissolved organic N (DON) in soil solutions. The simulated N deposition resulted in a significant increase in TDN, NOf and DON concentrations in soil solutions. The average CO_2 emission rate ranged from 222.6 mg CO_2 m~2 h~(-1) in CK to 233.7 mg CO_2 m~2 h~(-1) in the high-N treatment Three years of simulated N deposition had no effect on soil CO_2 emission, which was mainly controlled by soil temperature. The mean N_2O emission rate during the whole 3 years was 0.02 mg N_2O m~2 h~(-1) for CK, which increased significantly to 0.05 mg N_2O m~2 h~(-1) in the high-N treatment. The N_2O emission rate positively correlated with NH_4~+ concentrations, and negatively correlated with soil moisture. The average CH_4 flux during the whole 3 years was -0.74 ug CH_4 m~2 h~(-1) in CK, which increased to 1.41 μg CH_4 m~(-2) h~(-1) in the low-N treatment CH_4 flux positively correlated with NO3 concentrations. These results indicate that short-term N deposition did not affect soil CO_2 emissions, while CH_4 and N_2O emissions were sensitive to N deposition.