Effects Of Warming And Nitrogen Deposition On N₂O Emission In A Meadow In North Tibet

Climate warming and atmospheric nitrogen deposition are globally concerned research topics.As a regulator of global climate change,the Qinghai-Tibet Plateau safeguards the environment of China.With the economy development of South Asia,the long-distance transmission of nitrogen by the Indian monsoon has significantly has increased the atmospheric nitrogen deposition on the Tibetan Plateau.Over the past 50years,the temperature of the Qinghai Tibet Plateau has risen significantly,with a faster rate than the global average.N₂O is an important greenhouse gas,with a warming effect of 298 times as that of CO₂.With increases in temperature and nitrogen deposition,soil temperature is predicted to increase,and soil moisture to decline,and soil N content and availability to change.Such changes in soil are hypothesize to affect plant community structure,nutrient cycling and N₂O emission in alpine meadows.To clarify the mechanisms of warming and N deposition on N₂O emission in alpine meadows,in 2014 we set up experiments in alpine meadow with open-top chamber?OTC?to increase soil temperature by 2.4?and artificial nitrogen application(40 kg N·hm^-2·a^-1)to simulate nitrogen deposition increase.In 2018 and 2019,we observed and measured changes in plant community characteristics,soil nutrients and N₂O emissions in response to experimental treatments,temperature increase and nitrogen deposition increase.The main findings and conclusions are summarized as follow:1.Species richness and aboveground biomass have improved under nitrogen deposition.Nitrogen deposition increased significantly with the total aboveground biomass and aboveground biomass of cyperaceous by maximum of 3.4 times.Moreover,the Gramineae increased significantly with 1.4 times in 2018 with the warming.The aboveground biomass of legumes increased significantly with increase of 14.7 times under the warming and nitrogen deposition.Nitrogen deposition increased the species richness by 26.9%.Therefore,nitrogen deposition can promote the growth of cyperaceous and legume?P<0.05?.2.The trend of nitrogen deposition and warming in the future may increase the soil nutrient content and its availability.The contents of total nitrogen?TN?,ammonia nitrogen?NH₄-N?,nitrate nitrogen?NO₃-N?,microbial biomass carbon?MBC?and microbial biomass nitrogen?MNB?in soil increased significantly under the nitrogen deposition,with the maximum increase of 56.0%.The total nitrogen and ammonia-nitrogen contents in soil were significantly increased by warming,with a maximum increase of43.1%.The contents of total nitrogen,ammonia nitrogen,nitrate nitrogen and microbial biomass nitrogen increased significantly under warming and nitrogen deposition,with a maximum increase of 56.7%?P<0.05?.3.Soil enzyme activity was significantly increased by nitrogen deposition,warming and their interaction?P<0.05?.In 2018,the increase of soil enzyme activity had the maximum range,and the activity of soil nitrous oxide reductase?NOS?increased by 78%under warming and nitrogen deposition.In 2019,the increase of enzyme activity showed the largest trend,especially the increase of soil ammonia mono-oxygenase?AMO?activity by 137%under warming.4.The warming had no significant effect on N₂O emission in the growth season of the observed years.The nitrogen deposition has a promoting effect on N₂O emissions,in which N₂O emissions significantly increased by 77.4%compared with CK in 2018.The warming had no significant effect on soil N₂O emission.The warming and nitrogen deposition significantly increased the N₂O emissions in soil,in which the N₂O emissions in 2019 significantly increased by 106.6%compared with CK?P<0.05?.5.The soil temperature and humidity were the main factors controlling N₂O emission in alpine meadow,which explained the emission variation of 40.9%and 43.5%N₂O,respectively.The N₂O emission was positively correlated with the biomass of hybrid grass,leguminous biomass,nitrous oxide reductase activity,and the nitrogen content of soil microbial biomass.However,the N₂O emission in soil was negatively correlated with soil NH₄-N content and gramineous biomass.Overall,the N₂O emission of alpine meadow may further increase under global warming and nitrogen deposition in the future.Our study revealed the character of N₂O emissions,the mechanism in the impact of global warming and nitrogen deposition on N₂O in alpine meadow,which is of great scientific significance to predict the response of alpine meadow to global warming and the increase of atmospheric nitrogen deposition in the future.