Study On Degradation Characteristics And Health Assessment Of The Alpine Steppe In The Source Region Of The Yellow River

As the main grassland type on the Qinghai-Tibet Plateau,the alpine steppe plays an important role in the global carbon and nitrogen cycle,animal husbandry production,biodiversity conservation,and water conservation.The alpine steppe is a natural ecosystem consisting of multiple elements such as soil,grass,livestock,humans and microorganisms.Due to its own vulnerability,coupled with the unreasonable use of humans,the ecosystem has undergone different degrees of degradation.In this study,the most representative alpine steppe of Stipa purpurea in the Yellow River source area located in Maduo County,Qinghai Province was selected as the research area,and the plots with different degradation degrees were selected(undegraded,mildly degraded,moderately degraded,severely degraded and extremely degraded)to investigate plant communities,functional groups,species and the physical and chemical properties of soil in order to clarify the characteristics of community,functional groups and species in the degradation process of alpine steppe and their relationship between plants and soil physical and chemical properties.The purpose of this paper is to develop practical and scientific results by evaluating the health status of alpine steppes with different degradation degrees.The evaluation index system of alpine steppe health,this study provides a scientific basis for vegetation restoration and reconstruction in alpine grassland.The main results are as follows:1.The degradation of alpine steppe has a significant impact on plant communities.The dominant species of plants under different degradation gradients changed significantly,from mild to severely degraded.The dominant species of grassland gradually changed from Stipa purpurea and Kobresia humilis to hybrid grasses,and the dominant species under extreme degradation were the biomass of aboveground plants increased first and then decreased,but the aboveground biomass of slightly degraded grassland was 21.5% higher than that of non-degraded grassland;the coverage of community decreased significantly(P<0.05);the height of community decreased significantly(P<0.05),but the height of extremely degraded grassland community increased;the important value of community increased first and then decreased(P<0.05).2.The composition of the alpine steppe functional group has a significant response to grassland degradation.The richness and important value of the grass functional group increased first and then decreased with the degree of degradation(P<0.05),and the coverage decreased with the degree of degradation(P<0.05).The functional enrichment of miscellaneous grasses,Both the coverage and the important value increased first and then decreased with the degree of degradation,while the relative importance of the heterotic grass functional group increased with the degree of degradation.3.The species diversity of alpine steppe responded significantly to grassland degradation.With the degree of degradation,plant species richness,diversity and uniformity increased first and then decreased(P<0.05).From the undegraded stage to the extreme degradation stage,the species richness decreased from 16.40 to 8.20;the species diversity Shannon-Wiener index decreased from 2.9 to 1.75.4.Alpine steppe degradation has a significant impact on soil physical and chemical properties.Soil organic matter,total nitrogen,total phosphorus and pH showed a significant decrease(P<0.05)with the degree of degradation;soil bulk density increased significantly with the degree of degradation(P<0.05);soil aeration porosity increased with degradation.The trend was significantly lower(P < 0.05).5.During the process of alpine steppe,vegetation is closely related to soil.The total coverage of plant community was significantly positively correlated with soil aeration porosity,soil total nitrogen and soil organic matter(r value: 0.86,0.73,0.72);aboveground biomass and soil aeration porosity,soil organic matter,soil total nitrogen were significantly positive Correlation(r value: 0.69,0.6,0.55);vegetation total coverage,aboveground biomass and soil bulk density were significantly negatively correlated(r value:-0.84,-0.67);important values of each functional group were positively correlated with soil aeration porosity.The relationship was negatively correlated with soil bulk density.The results of redundant analysis indicated that grassland degradation first affected soil physical properties and then affected the composition of grassland community species and functional groups,resulting in a significant decrease in grassland productivity.6.Construct an alpine steppe health assessment index based on total coverage,biomass,grass plant frequency,community layer structure,grassland development,species richness and new rat hole density(Grassland Health)Index,GHI),using principal component analysis to calculate the index weights,the weights of each index are 0.1789,0.1599,0.1690,0.0784,0.1515,0.1696 and 0.0928 respectively.Through the cluster analysis of GHI,the health status of alpine steppe in the study area is divided.There are 4 grades,namely healthy grassland(GHI>0.77),sub-healthy grassland(0.59<GHI?0.77),unhealthy grassland(0.29<GHI?0.59),and collapsed grassland(0.09<GHI?0.29).