Response Of Soil Multifunction To Soil Microbial Changes With Alpine Meadow Degradation

Alpine meadows are sensitive to climate change due to their unique ecosystem.The mechanisms by which soil microbial diversity affects soil function under degradation need to be extensively explored.In this study,alpine meadows were selected from nondegraded meadows,moderately degraded meadows and severely degraded meadows in the hinterland of Sanjiangyuan area according to different degradation degrees.Based on soil microbial activity,carbon sequestration,nutrient accumulation and soil fertility accumulation were selected,six functional indicators including total N,total P,available P,hydrolytic N,DNA concentration and total soil organic C were selected to calculate soil multifunction,and soil microbial(bacteria and fungi)diversity and network complexity were calculated based on high-throughput sequencing results.The influence of soil microbial(bacteria and fungi)on soil multifunctionality under the degradation of alpine meadows were analyzed.The conclusions were summarized below:(1)Degradation of alpine meadow reduced the soil function.With alpine meadow degradation,soil water content significantly decreased,while p H and soil bulk weight content significantly increased,soil compactness increased,soil multifunctionality significantly decreased,and hydrolytic N,total N,total organic C and available P in soil function also showed a significant decreasing trend,indicating that meadow degradation led to the loss of soil function.Soil p H and soil bulk weight was negatively correlated with soil multifunctionality,and soil electrical conductivity and soil water content were positively correlated with soil multifunctionality.(2)Degradation of alpine meadow changed soil microbial composition and structure.In the composition of soil bacterial and soil fungal communities in alpine meadows,soil bacteria at the phylum level mainly consisted of Actinobacteriota,Proteobacteria,Acidobacteriota and Chloroflexi,and fungi at the phylum level mainly consisted of Ascomycota,Basidiomycota and Mortierellomycota.At the genus level,the dominant genera of soil bacteria were norank＿f＿＿norank＿o＿＿Vicinamibacterales,RB41,norank＿f＿＿67-14,and norank＿f＿＿Vicinamibacteraceae,and the dominant genera of soil fungi are Mortierella,Hygrocybea andunclassified＿p＿＿Ascomycota.The relative abundance of dominant bacterial and fungal phyla was different in different degradation due to the change of soil environment.The dominant genera of soil bacteria did no significant difference under different degradation,but the dominant genera of soil fungi was different under different degradation.In the functional compositions of soil bacteria and fungi in alpine meadows,bacterial functions were mainly consisted of metabolic function,environmental information process function and gene information process function,among which metabolic function account for the majority of bacterial functions,carbohydrate metabolism and amino acid metabolism played a major role in metabolic function,and fungal functions mainly consisted of saprophytic and symbiotic nutritional fungi.(3)Degradation of alpine meadow makes the function of soil bacteria redundant.Soil microbial diversity increased significantly with degradation,while soil bacterial functional diversity decreased significantly trend with functional redundancy.The complexity of soil bacteria in alpine meadow increased with degradation,the number of links,edge density and average degree of soil fungi increased,and the modularity index decreased,and this result was the similar to the change characteristics of soil bacterial and fungal diversity.The neutral community model revealed that the assembly mechanism of soil bacteria in alpine meadow mainly exhibited stochastic processes.(4)The increase of soil bacterial homogenization leads to soil functional redundancy.In alpine meadow,soil bacterial Shannon diversity and bacterial complexity were negatively correlated with soil multifunctionality,while bacterial functional diversity was positively correlated with soil multifunctionality,which showed that degradation drives soil bacterial homogenization and functional redundancy,making bacteria more closely linked to each other to resist adverse environmental conditions.By exploring the main influencing factors of soil multifunctionality revealed that external environmental factors have a greater influence on soil multifunctionality,and degradation resulting in decreased water content and increased clay content significantly changes the survival environment of microbial,causing an increase in bacterial diversity and decreasing soil multifunctionality,and among biological factors bacterial complexity,bacterial functional diversity and bacterial Shannon diversity significantly influence soil multifunctionality,while among the bacterial functions,metabolic functions significantly affect soil multifunctionality,and among the metabolic functions,the amino acid metabolic functions of high relatively abundance have a significant negative correlation with soil C and N.