Stimulated or Inhibited Response of Methane Flux to Nitrogen Addition Depends on Nitrogen Levels
Ruiying Chang, Xinyu Liu, Tao Wang, Na Li, Haijian Bing
Abstract
Abstract Upland forest soil is significant atmospheric methane (CH 4 ) sink that is suggested to be affected by increased nitrogen (N) availability, likely from N deposition or addition. However, the effect of N addition on upland soil CH 4 uptake and the underlying mechanisms remain unclear. Here, in a montane forest, frequent in situ sampling over three years revealed that this forest soil was a sink of atmospheric CH 4 with an uptake rate of 304.9 ± 26.9 mg CH 4 /m 2 /yr under ambient treatment. High N addition suppressed CH 4 uptake by 23.2% compared to ambient conditions, whereas low N addition stimulated CH 4 uptake by 35.6%. N addition did not change the monthly pattern of CH 4 flux, which was quite similar to the pattern of leachate dissolved organic carbon (DOC) concentrations from the organic layer. The linear relationship between the CH 4 flux and DOC concentration indicated increased CH 4 uptake with an increase in DOC. The induced decrease in CH 4 uptake under high N addition was partly related to the high soil N availability and partly contributed to a decrease in DOC due to high N addition. In contrast, the increased CH 4 uptake under temporarily low N addition was most likely correlated with a release in N limitation to CH 4 ‐oxidizing bacteria. These results indicated that the effect of N addition on CH 4 uptake was dependent on the level of N, and DOC could regulate CH 4 uptake in upland soil, which should be investigated in depth when understanding the responses of dynamic CH 4 fluxes to N additions.