Pulse Increase of Soil N(2)O Emission in Response to N Addition in a Temperate Forest on Mt Changbai, Northeast China

Nitrogen (N) deposition has increased significantly globally since the industrial revolution. Previous studies on the response of gaseous emissions to N deposition have shown controversial results, pointing to the system-specific effect of N addition. Here we conducted an N addition experiment in a temperate natural forest in northeastern China to test how potential changes in N deposition alter soil N(2)O emission and its sources from nitrification and denitrification. Soil N(2)O emission was measured using closed chamber method and a separate incubation experiment using acetylene inhibition method was carried out to determine denitrification fluxes and the contribution of nitrification and denitrification to N(2)O emissions between Jul. and Oct. 2012. An NH(4)NO(3) addition of 50 kg N/ha/yr significantly increased N(2)O and N(2) emissions, but their “pulse emission” induced by N addition only lasted for two weeks. Mean nitrification-derived N(2)O to denitrification-derived N(2)O ratio was 0.56 in control plots, indicating higher contribution of denitrification to N(2)O emissions in the study area, and this ratio was not influenced by N addition. The N(2)O to (N(2)+N(2)O) ratio was 0.41–0.55 in control plots and was reduced by N addition at one sampling time point. Based on this short term experiment, we propose that N(2)O and denitrification rate might increase with increasing N deposition at least by the same fold in the future, which would deteriorate global warming problems.