Effects Of Warming On Nitrogen Oxide Fluxes In The Peatland From Continuous Permafrost Zone, Great Hinggan Mountains

Peatland mainly distributes in the northen high latitude region,it is very sensitive to global warming.In the recent decades,northern high latitude region has experienced pronounced warming,resulting in degeration of the permafrost.The increasingly human activity has aggravated this change,which would directly or indirectly influence the cycle of carbon and nitrogen in peatland,potentially causing positive and negative feedbackes to climate changes.However,study on the effect of climate change on nitrogen cycle in continuous permafrost region is scare.Hence,a warming experiment using open-top chambers?OTC?in field and a incubation experiment were established in boreal peatland of permafrost region in Great Hing'an Mountains,focusing on both the effects of warming,freeze-thaw events and nitrogen availability on nitrogen oxides.The aim of this study was to clarify the temporal dynamics of nitrogen oxide emissions in the peatland,disuccssed the effects of warming on nitrogen oxide flux and the controlling factors,and explore the responses of N₂O flux on freeze-thaw events and nitrogen availability.The results were showed as follows:?a?During a warming experiment using Open Top Chambers?OTC?in field,the warming effects of soil surface temperature were higher than air temperature in peatland.Mean air temperature were 0.6? higher in warmed plots than the control plots,while soil temperature at 5cm depth,soil temperature at 10 cm depth,soil temperature at 20 cm depth,soil temperature at 30 cm depth,soil temperature at 50 cm depth,soil temperature at 100 cm depth were 2.42??1.48??1.21??0.57??0.45??0.48? higher in warmed plots than the control plots.The increased soil temperature lead to the mean soil active deeper increase by 6.6cm,while warming has a little effect on soil moisture.?b?Based on a warming experiment using Open Top Chambers?OTC?in field,warming increased N₂O flux significantly during each year of observation,increased by 89%-223%.The result showed that: on the scale of the year,the warming induced changes in N₂O fluxes of Betula fruticosa-Sphagnum mosses dominated peatland were 174%,128% and 167%,respectively;the warming induced changes in N₂O fluxes of Ladum palustre-Sphagnum mosses dominated peatland were 165%,123% and 122%,respectively.On the month scale,the warming induced changes in N₂O fluxes of Betula fruticosa-Sphagnum mosses dominated peatland was 223% in August,while the warming induced changes in N₂O fluxes of Ladum palustre-Sphagnum mosses dominated peatland was 217% in July.Soil temperature and soil active layer depth were the main factors influencing N₂O fluxes in peatland of the permafrost region.?c?Based on a warming experiment using Open Top Chambers?OTC?in field,warming increased NO flux significantly during each year of observation,increased by 75%-239%.The result showed that: on the scale of the year,the warming induced changes in NO fluxes of Betula fruticosa-Sphagnum mosses dominated peatland were 176%,226% and 133% in 2013,2014 and 2015,respectively;the warming induced changes in NO fluxes of Ladum palustre-Sphagnum mosses dominated peatland were 154%,177% and 127% in 2013,2014 and 2015,respectively.On the month scale,the warming induced changes in NO fluxes of Betula fruticosa-Sphagnum mosses dominated peatland was 239% in August,while the warming induced changes in NO fluxes of Ladum palustre-Sphagnum mosses dominated peatland was 219% in July.Soil temperature were the main factors influencing NO fluxes.?d?During the freeze-thaw incubation experiments,FT events and nitrate-N addition significantly enhanced the accumulation of N₂O emissions in boreal permafrost peatlands.We also observed pulses of N₂O emissions in all treatments under the FT condition,and the influence of FT events was pronounced in NS treatments.Emissions of N₂O were positively correlated to soil NO3-concentrations,thereby indicating that availability of nitrate-N and denitrification were responsible for enhanced N₂O emissions following FT events.The combined effects of FT events and nitrate-N addition on N₂O emissions are additive,which could stimulate more N₂O emissions in boreal permafrost peatlands?e?In the nitrogen availability incubation experiment,soil N₂O emission rates increased as the level of nitrogen addition increasing,nitrogen addition had a priming effect on N₂O emission,however,the priming effect of deep soil involved a time lag.Nitrogen addition influenced N₂O emission at 0-15 cm depth soil significantly,nitrogen addition treatments reached significant level compared with control.Nitrogen addition did not significantly influence N₂O emission at 15-30 cm depth,while only high nitrogen addition had significant effect on N₂O emission at 30-45 cm depth.