Characteristics Of Soil N₂O Emission And Its Main Influence Factor During The Freeze-thaw Period In Non-growing Season In Temperate Typical Grassland

N₂O is an important greenhouse gas.It stays in the atmosphere for 120 to 150 years,and its adverse effects after entering the atmosphere are difficult to eliminate in a short period of time.The proportion of N₂O emissions in soil accounts for a relatively high proportion of global N₂O emissions.In the past,soil N₂O emissions has focused on the growing season.Some studies have found that N₂O emissions at this stage cannot be ignored.With other ecosystems,studies on grassland soil N₂O emission characteristics and impact factors under different freezing and thawing periods and different snow cover conditions during the non-growth season of Chinese grassland ecosystems(approximately 40%of the country's land area)are scarce.Therefore,the impact of the changing characteristics of soil N₂O emissions on the atmospheric environment during the non-growth season and the different freezing and thawing periods of grassland ecosystems is a hot issue that needs to be studied in environmental science.The research results provide indispensable data support for the study of global warming trends,the establishment of grassland ecosystem N₂O gas emission inventory,and the establishment of grassland management systems,which have important theoretical significance and practical value.This paper takes temperate grassland as the research object and conducts field experiments(setting AS:snow increase,RS:snow removal,CK:environmental snow)to compare the soil N₂O in the whole non-growth season and under different freezing and thawing periods and different snow cover conditions.The characteristic changes of the emission flux and the difference in the cumulative flux size reveal the relationship between the changes of environmental factors(soil moisture,soil temperature,atmospheric temperature,ammonium nitrogen,nitrate nitrogen)and the soil N₂O emission flux.The main environmental factors affecting grassland soil N₂O emissions during the non-growth season.The main conclusions are as follows:(1)During the thawing-frozen season in autumn and winter,the N₂O emission flux in the soil ranges from 3.441±1.385?71.218±14.356ug·m^-2·h^-1.In this stage,the RS treatment showed a pulsed peak in N₂O emission after snowfall;N₂O emission flux in the winter period is 2.615±1.775?14.726±5.415ug·m^-2·h^-1;N₂O emission flux in the spring-winter freezing-thawing period is-2.161±2.611?13.220±1.546ug·m^-2·h^-1.The whole non-growth season,soil N₂O emission flux range is-2.161±2.611?71.218±14.356ug·m^-2·h^-1.Except for the thawing-freezing period in autumn and winter,there are significant differences in soil N₂O emission flux between three different snow treatments(P<0.05),and there are no significant differences soil N₂O emission between the other two stages and different snow treatments(P>0.05).(2)The cumulative N₂O emissions of the three treatments of RS?AS and CK in the whole non-growth season were 40.258±1.491mg·m^-2?33.537±1.963 mg·m^-2 and 33.421±2.075 mg·m^-2.The cumulative N₂O emission flux of soil in RS treatment was significantly greater than that of AS and CK(P<0.05),but the difference of cumulative N₂O emission between AS treatment and CK treatment was not significant(P>0.05).(3)The main control factors affecting soil N₂O emission flux are different in the AS treatment during each freezing and thawing period in the non-growth season.In the autumn-winter thawing-frozen period,soil N₂O is mainly affected by the soil moisture(0?10cm)content,y=-64.585+4.473x,p=0.781(P<0.05);in the winter complete freezing period,the soil N₂O emission flux is mainly controlled by the temperature of the soil surface(0cm),y=8.288+0.189x,p=0.654(P<0.05);and during the winter-spring freeze-thaw period,soil ammonium nitrogen and mineral nitrogen are the main factors affecting soil N₂O emissions Control factor,y=2.409+0.853x(ammonium nitrogen),p=0.753(P<0.01)?y=0.924+0.610x(mineral nitrogen),p=0.615(P<0.05).During the spring freeze-thaw period,the response of soil N₂O(peak)to changes in soil moisture(peak)after the snow melts is not synchronized,but has a certain lag in time.However,there was no significant correlation between N₂O emission flux and environmental factors(atmospheric temperature,soil temperature,moisture,ammonium nitrogen,nitrate nitrogen)in each freezing and thawing period of CK and RS treatment(P>0.05).