Investigation And Analysis On The Degradation Characteristics Of Alpine Meadows In Qilian Mountain National Park

Qilian Mountains National Park is located on the northeast edge of the ecological barrier zone of the Qinghai-Tibet Plateau in China’s "Three Zones and Four Belts" strategy,north of the northern sand barrier,and is one of the important nature reserves in China with a very important ecological security status.In China,the construction of ecological civilization is a major issue related to people’s livelihood.Promoting ecological protection research in the Qinghai-Tibet Plateau ecological barrier zone is in line with national ecological restoration policies and goals,helps maintain the balance of the ecosystem,and promotes the construction of a "Beautiful China" and harmonious coexistence between humans and nature.Alpine meadow is the main grassland type in Qilian Mountains National Park,and grassland degradation directly affects its ecological barrier function.Therefore,this study selected alpine meadows with different degrees of degradation in Qilian Mountains National Park as the research object and explored the vegetation and soil characteristics of alpine meadows with different degrees of degradation through field sample surveys,measurement of aboveground biomass,physical properties,and nutrient contents of soil,soil enzyme activity,and soil microbial community structure,and correlation analysis,redundancy analysis,and the use of multiple vegetation and soil indicators,to explore the vegetation and soil characteristics of alpine meadows with different degrees of degradation,to reveal the health status of grassland plants and soil,and providing a theoretical basis for the rational utilization and ecological restoration of the Qilian Mountains alpine degraded grassland ecosystem.The main research conclusions were as followed:(1)In Qilian Mountains National Park,the vegetation of undegraded alpine meadows was mainly Cyperaceae and Gramineae,and with the increase of degradation degree,Gramineae plants were gradually replaced by Leguminosae and miscellaneous grasses(such as Compositae),and the height,coverage,aboveground biomass and species diversity index of plant communities were decreasing.(2)With the aggravation of degradation degree,soil moisture content,total porosity,available nitrogen content,available phosphorus content,available potassium content,total nitrogen content,total phosphorus content,total potassium content,and organic matter content gradually decreased,while soil bulk density and p H gradually increased in alpine meadows.Compared with undegraded alpine meadows,severely degraded alpine meadows had a 61.3%and 43.8% decrease in soil moisture content and organic matter content,respectively,and a37.8% increase in soil bulk density.The composition of soil aggregates changed in alpine meadows with different degrees of degradation,with aggregate sizes gradually shifting from larger to smaller diameters.The mean weight and geometric diameter of soil aggregates decreased,and soil stability decreased.Correlation analysis showed a significant correlation(P<0.05)between plant characteristics and soil physical and chemical properties,with vegetation cover and aboveground biomass being most affected by soil bulk density,moisture content,total porosity,and available phosphorus content.(3)During the degradation of alpine meadows,soil urease activity,sucrase activity,phosphatase activity,and catalase activity all showed a decreasing trend.(4)At the phylum level,the dominant bacterial groups in alpine meadow soils with different degrees of degradation were Proteobacteria,Actinobacteria,Acidobacteria,and Chloroflexi,with relative abundances of 25.31%-33.8%,23.75%-33.55%,16.78%-19.96%,and 9.10%-11.58%,respectively.The dominant fungal groups in soil were Ascomycota,Basidiomycota,and Mortierellomycota,with relative abundances of 50.49%-73.53%,9.34%-26.50%,and 1.67%-4.42%,respectively.The degradation of alpine meadows significantly affected the soil bacterial community structure,while its impact on the soil fungal community structure was relatively small.Correlation analysis showed that the dominant microbial groups and relative abundances of bacterial and fungal communities in soil were intrinsically related to soil properties and vegetation characteristics.Changes in vegetation and soil properties caused by grassland degradation have different effects on different soil bacterial and fungal community compositions.There is a significant correlation between bacterial community and soil physicochemical properties,and there is a significant positive correlation between bacterial community and soil available phosphorus content and soil available potassium content(P<0.05).There is a significant correlation between fungal communities and vegetation and soil physicochemical properties,and a significant positive correlation with aboveground biomass,MWD,and GMD of vegetation(P<0.05).