The Interaction Of Vegetation-soil-microbes In The Degradation Process Of Alpine Grassland In Qilian Mountains Of China

Alpine grassland is an important component of terrestrial ecosystems and a key barrier to maintaining national ecological security.Due to the long-term unreasonable utilization,the region is faced with serious ecological problems.Aiming at the current situation of grassland degradation and problems,which has been in the aspect of degraded alpine grassland degradation characteristics and mechanism to do a lot of research.However,these studies only studied from the perspectives of“soil-microbes”or“soil-vegetation”,and lacked the combination of“vegetation-soil-microbes”as a whole,and in-depth exploration of the internal interaction rules to study the mechanism of grassland degradation.Therefore,this study took the alpine degraded grassland in Qilian Mountains as the research object,and analyzed the changes of vegetation,soil characteristics and soil microbial community structure through the method of spatial scale instead of time scale was used to analyzed the process of grassland degradation?non-degraded grassland,lightly degraded grassland,moderately degraded grassland and severely degraded grassland?.The classical statistical methods such as principal component analysis,correlation analysis,redundancy analysis and structural equation modeling were used to reveal the interaction relationship between“vegetation-soil-microbes”in the degradation process of alpine grassland in Qilian Mountains.It provided theoretical basis and practical guidance for the restoration,management and protection of alpine grassland ecosystem in Qilian Mountains.The main results are as follows:?1?The dominant species in the alpine degraded grassland of Qilian Mountains were mainly Cyperus rotundus,Polygonum viviparum and Leymus secalinus.Vegetation height,aboveground biomass and coverage showed a downward trend during grassland degradation.The plant functional group was dominated by forb,followed by Cyperaceae,and the least was Gramineae.Cyperaceae and Gramineae showed downward trend,while forb showed an increasing trend;?2?During the degradation of alpine grassland,the soil pH and EC increased,and the contents of SOC,TP,TN,AP,NO₃^--N,NH₄⁺-N and AN decreased gradually.?3?In the degradation process of alpine grassland in Qilian Mountains,soil enzyme activities?catalase,invertase,alkaline phosphatase,urease,cellulase?and soil microbial biomass?MBC,MBN,MBP?shown decrease trend;?4?The soil C/N of different degraded grassland in Qilian Mountains were 17.16-63.20,which was higher than the average value?10-12?of land soil in China;soil C/P were78.13-181.19,higher than the average C/P value?24.45?in alpine grasslands;soil N/P were3.86-8.31;MBC/MBN were 1.48-7.61,MBC/SMBP were 4.02-20.54,and MBN/MBP were1.63-3.34;?5?The dominant bacterial community in the alpine degraded grassland of Qilian Mountains were Proteobacteria,Actinobacteria,Acidobacteria,Gemmatimonadetes,Campylobacter,Chloroflexi and Firmicutes;the dominant fungal community were Streptophyta,Ascomycota,Basidiomycota,Glomeromycota,unclassified_dEukaryota and Chordata;the mainly dominant archaea communities were Euryarchaeota,Thaumarchaeota,Candidatus_Bathyarchaeota and Crenarchaeota.The dominant bacterial genera of different degraded alpine grasslands were Pyrinomonas,unclassified_cBetaproteobacteria,unclassified_pAcidobacteria,Solirubrobacter,unclassified_dBacteria,unclassified_pCandidatus_Rokubacteria,Bradyrhizobium and Gemmatimonas;The dominant fungal genera were Rhizophagus,Pantholops,Acanthamoeba,Beta and Exaiptasia;the dominant archaea genera were Nitrososphaera,Candidatus_Nitrosocosmicus,unclassified_dArchaea,Methanosarcina,unclassified_oThermoplasmatales and unclassified_pCandidatus_Bathyarchaeota,but the relative abundance of soil microbial communities varies among different degraded grassland.The PCoA and NMDS analysis shown that the soil microbial community varied greatly in various plots during the degradation of alpine degraded grassland in Qilian Mountains.A number of comparative analysis found that the most significant differences were Nitrospirae,Candidatus_Tectomicrobia,and Thaumarchaeota.LefSe analysis shown that the soil microbial community structure in different degraded grassland was significantly different,and the whole showed bacteria>fungi>archaea;?6?In the degradation process of alpine grassland in Qilian Mountains,vegetation changes significantly affected soil physical and chemical properties?soil pH,EC,TP,TN,NO₃^--N and AN content?,soil biological properties?soil invertase,cellulase,MBC,MBN,MBP?and ratio of ecological stoichiometry?MBC/MBN,MBC/MBP and MBN/MBP?;the main factors affecting the distribution of soil bacterial communities were SOC,AP,TP,TN,soil catalase,invertase,urease;alkaline phosphatase,MBC,MBN,MBP,C/N,C/P,N/P,MBC/MBN and MBN/MBP;the main factors affecting the distribution of soil fungal communities were soil pH,EC,AP NH₄⁺-N,AN,soil urease,alkaline phosphatase,vegetation evenness index,Shannon-Wiener index and frequency;the main factors affecting the distribution of soil archaea communities were soil pH,AP,NH₄⁺-N,EC,NO₃^--N,AN,soil invertase,alkaline phosphatase and C/P.The results of structural equation model showed that the changes of soil microbial community structure were mainly affected by soil properties and vegetation characteristics during the degradation of alpine grassland in Qilian Mountains.Both vegetation and soil physical and chemical properties had a positive effects on soil microbial community structure changes,with cumulative impacts of 0.58 and 0.76,respectively.And soil properties had the greatest influence on soil microbes.In addition,changes in soil microbial communities adversely affect vegetation and soil properties.In summary,the results showed that in the degradation process of alpine grassland in Qilian Mountains,plants,soil and soil microbes interact and interact with each other.Grassland degradation directly affects the distribution of surface plants,which in turn affects soil properties and soil microbes.Conversely,soil microbial community structure changes cause changes in soil properties and affect vegetation characteristics.