Effects Of Climate Change On Above-Ground Biomass And Greenhouse Gases In Qinghai Province Grassland

As one of the largest terrestrial ecosystems type,grassland covers about 20%of the total land area in the world.Grassland not only plays an important role in providing natural resources and ecological barriers,but also provides the material basis for the development of grassland animal husbandry.In recent years,due to the increasing global greenhouse effect caused by human activities on the ecosystem,the response of grassland ecosystem biomass and its carbon and nitrogen cycle to global climate change has become one of the current research hotspots.Based on models,exploring the effects of climate change,soil conditions,management methods and other factors on grassland above-ground biomass（AGB）and greenhouse gas emissions（GHG）is a vital approach to understanding the response of grassland carbon dynamics on global climate change.Based on 15 years（2005-2019）of above-ground biomass data,this study used with geochemical model DNDC to simulate the changes in grassland biomass and greenhouse gases in Qinghai Province under different nitrogen deposition scenarios and future climate scenarios.The main research results are as follows:1.The key parameters of simulated biomass and greenhouse gas emissions by the DNDC model were adjusted according to the measured data of AGB and GHG about different grassland types in Qinghai Province.After parameter optimization,the R² between simulated and observed of AGB CO₂,CH₄,N₂O in Qinghai Province grassland is 0.64,0.75,0.67,0.53,respectively.The above results indicate that the DNDC model has good expansibility both in time and space,and can better simulate AGB and GHG in Qinghai Province.2.The average AGB range of above-ground biomass in Qinghai Province from 2005 to2019 was 0-2798.15 kg DW ha^-1 y^-1.In the past 15 years,most of the grassland areas were no significant change overall,but the significant increase in area accounted for 6.4%of Qinghai Province,mainly distributed in from the Kunlun Mountain to Bayankhara Mountain range,Qilian Mountain range,southern and eastern Qinghai Mongolian Autonomous County in Henan Province,Huangnan Tibetan Autonomous Prefecture and southern Yushu Tibetan Autonomous Prefecture.3.The increase of nitrogen deposition increased 3-75%of AGB,decreased 5-30%of CO₂emissions,and increased 400-5000%of N₂O emissions in Qinghai Province grassland.There was a non-significant correlation between CH₄ uptake and nitrogen deposition.In addition,nitrogen deposition changes the spatial distribution pattern of the correlation between global warming potential（GWP）and temperature and precipitation.With the increasing nitrogen deposition,the areas where GWP is negatively correlated with temperature and positively correlated with precipitation increased significantly.4.The AGB,CO₂ and N₂O emission,CH₄ uptake,of grassland in Qinghai Province were significantly increased under different future climate emission scenarios（P<0.001）.With the change of future climate scenario（from SSP1-2.6 to SSP5-8.5）,AGB,CO₂,N₂O emissions and CH₄ absorption will increase significantly.Compared with SSP1-2.6,AGB,CO₂ emission,CH₄ absorption and N₂O emission increased by 38.9%,40.6%,41.3%and 27.3%respectively under SSP5-8.5.The AGB,CO₂ and N₂O emission,and CH₄ uptake showed a significant increasing trend with time under SSP1-2.6,SSP2-4.5 and SSP3-7.0 scenarios.In spatial,the trend of AGB,CO₂ emission and CH₄ uptake of grassland in Qinghai Province grassland is decreased in the western region and increased in the eastern region.With the change of emission scenario（from SSP1-2.6 to SSP5-8.5）,the proportion of areas in which AGB,CO₂emission and CH₄ uptake of grassland increased significantly over time and the proportion of areas in which N₂O emission decreased significantly over time increased.5.Under the combined influence of nitrogen deposition and future climate change,future climate change has an extremely significant effect on AGB,CO₂ emissions and CH₄uptake（P<0.001）.While nitrogen deposition has an extremely significant effect on N₂O emission and GWP（P<0.001）.Nitrogen deposition and future climate scenarios had non-significant interaction effects on grassland AGB,GHG and GWP in Qinghai Province.In general,based on the optimized DNDC model parameters,which are suitable for simulating grassland biomass and greenhouse gas emission in Qinghai Province,this study compared the variation trends of AGB and GHG in Qinghai Province under different nitrogen deposition scenarios and future climate scenarios.With global warming,the cold and rain-less climate of high altitude in Qinghai Province was improved.The AGB of grassland in this region increased with the increasing temperature and precipitation,and the GHG also showed an increasing trend.Therefore,the increase of temperature and frequency of extreme precipitation events is conducive to the AGB accumulation in Qinghai Province.The effects of nitrogen deposition on AGB and GHG of grassland in Qinghai Province are less significant than those of future climate change,but the effects in the future cannot be ignored.Therefore,controlling the increase of nitrogen deposition and future drastic climate change can improve the AGB of grassland and reduce GHG in Qinghai Province,which has a positive effect on maintaining the stability and sustainability of grassland ecosystem in Qinghai Province.