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

Abstract Freeze-thaw (FT) events and increasing nitrogen (N) availability may alter N turnover and nitrous oxide (N 2 O) emissions in permafrost peatlands. However, the responses of N 2 O 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 N 2 O under FT and non-freeze-thaw (NFT) conditions in boreal peatlands of Northeast China. Results indicated that the FT condition significantly increased N 2 O emissions compared with the NFT condition and peaks occurred during thawing. Compared with AC treatments, NS treatments significantly elevated the accumulation of N 2 O emissions under the FT condition, exhibiting significant differences in different NS levels. N 2 O emissions were also positively dependent on soil NO 3 − concentrations to supply nitrate for denitrification. Nitrate-N addition was mainly responsible for the burst of N 2 O with denitrification as the main process during FT events. Therefore, these results suggest that N 2 O emissions potentially increase during FT events with increasing nitrate-N deposition in permafrost peatlands, which would contribute to global climate warming.