Effect Of Warming On N₂O Emission On Alpine Meadow And Cultivated Grassland In The Qinghai Tibet Plateau

As large amount of fossil fuels were burned since the second industrial revolution,rising concentrations of greenhouse gases in the atmosphere caused global warming.As an important greenhouse gas,N₂O has 298 times single molecular warming potential of CO₂.Qinghai Tibet Plateau is an important ecological security barrier in China,and its warming rate is far more higher than the average of China.Alpine grassland ecosystem not only supports the regional ecological security,but also is the basis of animal husbandry for Tibetan herdsmen.In response to the seasonal shortage of forage,the area of cultivated grassland has increased in recent years on Qinghai Tibet Plateau.Thus,this study carried out a simulating warming experiment on alpine meadow and cultivated grassland ecosystem,to reveal the response of N₂O emission flux to climate warming,and discuss the N₂O emission mechanism of alpine meadow and cultivated grassland.This study will provide basic data and theoretical basis for the establishment of adaptive management of alpine meadow and cultivated grassland.This study was carried out on the alpine meadow and cultivated grassland ecosystem on Qinghai Tibet Plateau.Open top chambers were used to simulate climate warming on grassland.The experiment was carried out from June 2018 to September 2019,including two treatments as warming?W?and control check?CK?.Each treatment was repeated four times,as a total of 16 plots.We measured soil temperature and humidity,N₂O emission flux,soil carbon pool,soil nitrogen pool and soil enzyme activity.The response of and soil progress impacts on N₂O emission fluxes were analyzed on different grassland types in response to warming.The main results are:?1?Warming promoted the N₂O emission of alpine meadow and cultivated grassland in Qinghai Tibet Plateau,with increases of 82.9%and 67.9%respectively on annual average;in alpine meadow and artificial grassland,the N₂O emission fluxes in growing season were 4.67 times and 1.48 times of that in non growing season,respectively?P<0.05?;in growing season,alpine meadow and cultivated grassland had no significant difference of the N₂O emission fluxes?P>0.05?.?2?Warming had significant impacts on the soil process,especially on soil enzyme activity.Warming significantly promoted the activities of Hao,AMO,NXR,NOR and NOS in the growing season of alpine meadow and cultivated grassland?P<0.05?.In alpine meadow,warming increased soil enzyme activity by 22%-43%,among which NOS activity increased most by 42.4%.In cultivated grassland,warming increased soil enzyme activity by 24%-45%,among which AMO activity increased most by 44.5%.?3?In the growth season of 2019,the increase of temperature significantly increased the soil dissolved organic carbon content of alpine meadow?P<0.05?,with an increase of 24.9%,but had no significant effect on the soil total carbon and dissolved organic carbon content of artificial grassland?P>0.05?.In growth season of 2018,warming significantly reduced the total nitrogen content in alpine meadow and cultivated grassland?P<0.05?,by 25.0%and 17.3%respectively.Warming significantly increased the content of nitrate nitrogen in alpine meadow and cultivated grassland?P<0.05?,by27.5%and 17.5%respectively.?4?Soil process had important impacts on the response of N₂O emission flux to climate warming in alpine meadow and cultivated grassland.In alpine meadow,N₂O emission flux was positively correlated with soil temperature,soil enzyme activity,soil dissolved organic carbon and nitrate nitrogen?P<0.05?.In the cultivated grassland,N₂O emission flux was positively correlated with soil enzyme activity,dissolved nitrogen and nitrate nitrogen content?P<0.05?.However,N₂O emission flux had significant negative correlation with soil dissolved organic carbon.According to the principal component analysis,N₂O emission flux could mainly affected by the activities of HAO,NOS,NOR and NXR,dissolved nitrogen in alpine meadow.And N₂O emission flux could mainly affected by the activities of HAO,NOS,NOR,NXR,AMO,ammonium nitrogen,total nitrogen and nitrate nitrogen in cultivated grassland ecosystem.In conclusion,N₂O emission flux may increase on alpine grassland ecosystem in Qinghai Tibet Plateau under climate warming,which could had a positive feedback to climate change and enhance warming.Thus,future study should focus on the adaptation technology of N₂O emission reduction,and government should enhance grassland management,in order to mitigate climate warming.