Rapid N2O fluxes at high level of nitrate nitrogen addition during freeze-thaw events in boreal peatlands of Northeast China

Freeze-thaw (FT) events and increasing nitrogen (N) availability may alter N turnover and nitrous oxide (N2O) emissions in permafrost peatlands. However, the responses of N2O emissions to different N levels and additions during FT events are far from clear. We conducted an incubation study to investigate the impacts of different N addition levels (LN: 0.07 mg N g(-1), HN: 0.14 mg N g(-1)) and N addition forms (AC: ammonium chloride, NS: sodium nitrate) on the emissions of N2O under FT and non-freeze-thaw (NFT) conditions in boreal peatlands of Northeast China. Results indicated that the FT condition significantly increased N2O emissions compared with the NFT condition and peaks occurred during thawing. Compared with AC treatments, NS treatments significantly elevated the accumulation of N2O emissions under the FT condition, exhibiting significant differences in different NS levels. N2O emissions were also positively dependent on soil NO3- concentrations to supply nitrate for denitrification. Nitrate-N addition was mainly responsible for the burst of N2O with denitrification as the main process during FT events. Therefore, these results suggest that N2O emissions potentially increase during FT events with increasing nitrate-N deposition in permafrost peatlands, which would contribute to global climate warming. (C) 2016 Elsevier Ltd. All rights reserved.