Effects Of Grazing And Climate Change On Plant Community And Soil Organic Carbon In Stipa Breviflora Steppe

The Stipa breviflora desert steppe is a distinct grassland type.Due to its unique geographical location and vegetation type,grazing has become an important way of utilization.However,unjustified grazing will lead to vegetation degradation and loss of soil organic carbon.In recent years,climate change has been affecting the steppe at an unprecedented rate.Although a large number of studies have reported the effects of grazing and climate change on a desert steppe,the effects of the interaction between grazing and climate change on aboveground standing biomass of plant community and soil organic carbon stock of desert steppe are still unclear.Therefore,through a long-term grazing experimental conducted in the region,combined with the Soil Plant and Atmosphere Continuum System（SPACSYS）model,the changes in aboveground standing biomass of plant community and soil organic carbon stock under different climate scenarios and stocking rates were predicted,aiming to develop reasonable grazing practice for a desert steppe,and provide a scientific basis for the sustainable development of steppe and mitigating climate change.The long-term grazing experiment was arranged in a randomized complete block design,with four stocking rates and three replicates,each the stocking rates were set as no grazing（NG）,light grazing（LG）,moderate grazing（MG）and high grazing（HG）,which the stocking rates were 0,0.91,1.82 and 2.71 sheep ha^-1half^-1 year^-1,respectively.The main conclusions of this study are as follows:（1）Richness of plant community was significantly decreased by 16.28%,30.91%,and 44.93%under the light,moderate,and high stocking rates,respectively（P<0.05）.The light,moderate,and high stocking rates significantly reduced the coverage of the plant community by 16.25%,39.46%,and 55.16%（P<0.05）.Aboveground standing biomass significantly decreased by 15.15%,38.72%,and 55.80%under the light,moderate,and high stocking rates,respectively（P<0.01）.（2）There was a significant positive correlation between annual precipitation and richness of the plant community（y=0.12+0.01x,R²=0.53,P<0.05）,while there was no significant correlation between annual temperature and richness of the plant community.There was a correlation between annual precipitation and aboveground standing biomass,the relationship was y=8.63+0.44x（R²=0.62,P<0.05）.There was no significant correlation between the annual temperature and aboveground standing biomass.There was no significant correlation between annual precipitation or temperature and soil organic carbon stock.（3）Model calibration with the observed data on aboveground standing biomass in NG from 2013 to 2019 and soil organic carbon stock from 2014 to 2017 suggested the SPACSYS model performed well（R²=0.70,KGE=0.75 and PBIAS=-1.30%for standing biomass,R²=0.89,KGE=-1.48 and PBIAS=-1.20%for soil organic carbon stock）.The model was subsequently validated using the observed data on aboveground standing biomass and soil organic carbon stock at the light,moderate,and high stocking rates,which also showed acceptable performance.（4）Under the Representative Concentration Pathways 2.6,4.5,and 8.5 climate scenarios,grazing at the moderate and high stocking rates resulted in more aboveground standing biomass loss,while grazing with the light stocking rate resulted in less aboveground standing biomass loss.In addition,grazing at the light stocking rate increased soil organic carbon stock,while moderate and high stocking rates decreased soil organic carbon stock.Therefore,grazing at a light stocking rate is a reasonable grazing management for the desert steppe,which can maintain high productivity and increase carbon sink to mitigate climate change,thus fully exploiting the productive and ecological functions of steppe.