Pulse Increase of Soil N2O 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.