Different Stocking Rates On Spatial Distribution Characteristics Of Shrubs And Semi-shrubs In Stipa Breviflora Desert Steppe

Desert steppe occupies a unique position in the transition from steppe to desert in the Eurasian steppe.Due to the dual effects of climate change and human activities,the phenomenon of grassland shrub is widespread in desert steppe.Grazing is an important way for humans to use grassland.Under different grazing conditions,the feeding and trampling of livestock will cause spatial heterogeneity of shrubs and semi-shrubs in the ecosystem.Spatial heterogeneity refers to the non-uniform distribution of variables in space,which is a comprehensive reflection of patchiness and gradient.By analyzing the spatial distribution characteristics of shrubs and semi-shrubs in desert steppe,the degree of patching of different plant species under grazing disturbance can be studied,which is of great significance for understanding the succession mechanism of plant communities in desert steppe.This study was based on a long-term controlled stocking rate test platform（2004-2022）.Four different stocking rates(no grazing,CK,0 sheep·hm^-2·half year^-1;light grazing intensity,LG,0.93 sheep·hm^-2·half year^-1;moderate grazing intensity,MG,1.82 sheep·hm^-2·half year^-1;heavy grazing intensity,HG,2.71 sheep·hm^-2·half year^-1)were set up using a completely randomized block design.And two sampling scales（2.5m×2.5m,5m×5m）were used to study the density,height,coverage and aboveground biomass of shrubs（Caragana microphylla）,semi-shrubs（Ceratoides latens）and semi-shrubs（Artemisia frigida and Kochia prostrata）（hereinafter referred to as’shrubs and semi-shrubs’）in the experimental area by geostatistical methods.At the same time,the soil nutrient indexes adjacent to plant populations under different stocking rates were measured.The main results are as follows:（1）In 2021 and 2022,the increase of spatial scale increased the characteristic values of shrub and semi-shrub populations in desert steppe.With the increase of stocking rate,the density showed a linear downward trend,the height,coverage and aboveground biomass showed a stepwise or exponential decline,and the density of quinoa in HG treatment,approached zero.（2）Stocking rate had a great influence on the spatial heterogeneity of shrubs and semi-shrubs in desert steppe.The spatial distribution of different plant populations was mainly affected by structural factors（except for the density of Kochia prostrata）,which was spatially reflected in the distribution characteristics of patches or bands.Until the HG treatment,the spatial heterogeneity is weakened.The spatial heterogeneity of shrub and semi-shrub functional group density was the largest in CK treatment,and the spatial heterogeneity of height,coverage and aboveground biomass was the largest in LG treatment.The density of Artemisia frigida and Kochia prostrata is more sensitive to the response of stocking rate.With the increase of stocking rate,the density is affected first,then the coverage and aboveground biomass,and finally the height.The quantitative characteristics of Caragana microphylla showed the largest spatial heterogeneity in LG treatment,and the quantitative characteristics of Ceratoides latens showed the largest spatial heterogeneity in MG treatment.With the increase of spatial scale,the spatial heterogeneity of different plant populations becomes more obvious.（3）Stocking rate changed the soil nutrient content adjacent to different shrubs and semi-shrubs（P<0.05）,and the soil nutrient content decreased with the increase of soil depth.The total nitrogen content of adjacent soil of near different shrubs and semi-shrubs decreased with the increase of stocking rate.The soil organic carbon content near Artemisia frigida was the highest in CK treatment,and the soil organic carbon content near Kochia prostrata,Caragana microphylla and Ceratoides latens was the highest in LG treatment.The content of available phosphorus near Artemisia frigida,Kochia prostrata and Ceratoides latens was the highest in LG treatment,and the content of available phosphorus near Caragana microphylla was the highest in HG treatment.（4）Under different stocking rates,the height,coverage and aboveground biomass of shrub and semi-shrub plant populations were positively correlated with soil organic carbon.In summary,the increase of stocking rate will reduce the quantitative characteristic value of shrubs and semi-shrubs in the desert steppe of Inner Mongolia.Light grazing increases the spatial heterogeneity of shrubs and semi-shrubs and soil nutrient content.Heavy grazing reduces the spatial heterogeneity of plant populations.