Responses Of Alpine Meadow Vegetation,Soil And Microorganism To Altitudes And Aspect In Eastern Qilian Mountains And Its Microbial Adaptation Mechanisms

The Qilian Mountain is an ecological security barrier in Northwest of China,and alpine meadow is the main grassland type of Qilian Mountain,which has played a importance role in maintaining the stability of the Qilian Mountains ecosystem.However,due to climate changes and unreasonable use by humans,the alpine meadows had been seriously degraded in this area.In the context of global warming and the complex terrain Qilian Mountains,alpine meadows productivity changes caused by micro-environments,such as altitude and aspect,which have not received sufficient attention.The equal amount of grazing after pasture contracting has further accelerated the degradation of alpine meadows.The evolution of altitude and aspect jointly affects the characteristics of grassland plants,soil physical structure,nutrient and trace element content,and the characteristics of soil microbes.Clarifying the adaptation mechanism of grassland "vegetation-soil-microbe" to the evolution of altitude and aspect has important ecological significance for grassland management and utilization.The study taking the alpine meadows in the Jinqiang River Basin of the Eastern Qilian Mountains as the research object,and analyzes changes of the altitudes(2800m,3000 m,3200m,3400 m,3600m,3800 m and 4000m)and aspect(sun aspect,shady aspect)in alpine meadow vegetation,soil and microbial community structure,combined with mathematical statistical methods to reveal the“vegetation-soil-microbial”.At the same time,based on the molecular ecological network model,ours research explores the adaptation mechanism of alpine meadow soil microorganisms to changes in altitude and aspect,which can provide theoretical basis and practice for the rational management and ecological restoration of the Qilian Mountains alpine meadow ecosystem.The main results are as follows:1)With the altitude gradient increased,vegetation coverage,grass layer height,above-ground biomass,Cyperaceae,Leguminous and Fork biomass were first increased and then decreased,while Gramineae aboveground biomass decreased.In same altitude gradient,the vegetation coverage,grass layer height,aboveground biomass,Cyperaceae,Gramineae,and Leguminous aboveground biomass of shade aspects were higher than that of sunny aspects,while the biomass of Forks in sunny aspects was higher than that in shade aspects.The changes of Shannon-wiener Index and richness index was basically similar to above-ground biomass.2)With the increased in altitude,the soil water content,total porosity and water holding capacity were first increase and then decrease,but soil bulk density was first decreasing and then increases.In same altitude gradient,soil water content,total porosity and water holding capacity of shady aspects were higher than that of sunny aspects,and soil bulk density of shady aspects was lower than that of sunny aspects.With the increased in altitude,soil electrical conductivity,SOC,total N,total P,available N,available P and available K were first increase and then decrease,and total K was first decreases and then increases.In same altitude gradient,soil electrical conductivity,available K,total P and available K were lower than that of shady aspect,and below the altitude of 3200 m of SOC,total N,and available N in the sunny aspect were lower than that in shady aspect.The soil C/N,C/P and N/P of alpine meadows at different altitudes and aspect were 14.55-38.13,12.61-87.94 and 0.27-5.01.With the altitude increases,the soil C/N was first decreasing and then Increase,and C/P and N/P were opposite to C/N.In same altitude gradient,altitude below 3400 m of soil C/N,C/P and N/P on sunny aspects were lower than that in shady aspects,that is,the productivity of alpine meadows was mainly limited by soil nitrogen,and it was more serious in low and high-altitude areas.With the increase in altitude,soil urease,catalase,NAG and PPO were decreased,and alkaline phosphatase,LAP,AP,BG and POD were first increased and then decreased.In same altitude gradient,urease,catalase and NAG in sunny aspect were higher than that in shady aspect,and altitude below 3800 m of the soil alkaline phosphatase,LAP,AP and PPO enzyme activities were lower than that in shady aspect.3)The dominant phyla of soil fungal communities in alpine meadows at different altitudes and aspects were Basidiomycota,Ascomycota and Mortierellomycota,and the dominant were Agaricomycetes,Dothideomycetes and Archaeorhizomycetes.Shannon index and Chao1 index of soil fungi were first increase and then decrease with the increase of altitude.In ame altitude gradient,except 3800 m and 4000 m altitude,Shannon index and Chao1 index in sunny aspect were higher than that in shady aspect.LEf Se analysis found that,167 fungi species of different classification levels were screened from the alpine meadow soil at different altitudes and aspects.Fun Guild software function annotation found that,the alpine meadow soil fungi were mainly divided into 8 ecological functional groups.RDA and Mantel analysis found that,SOC,total N,soil bulk density,water content,POD,AP,Co,Mn,grass layer height,gramineous biomass were the main factors affecting fungal communities.The dominant phyla of soil bacterial communities in alpine meadows at different altitudes and aspects were Proteobacteria,Actinobacteriota and Acidobacteria,and the dominant were Alphaproteobacteria,Gammaproteobacteria and Thermoleophilia.Shannon index and Chao1 index of soil bacterial were first increase and then decrease with the increase of altitude.In ame altitude gradient,Shannon index in sunny aspect was higher than that in shady aspect,and altitude sunny aspect beiow 3400 m of Chao1 index was lower than that in shady aspects.LEf Se analysis found that,167 bacterial species of different classification levels were screened from the alpine meadow soil at different altitudes and aspects.FAPROTAX software function annotation found that,soil bacteria in alpine meadows were mainly divided into 12 ecological function groups,which was mainly aerobic＿ammonia＿oxidation and chemoheterotrophy.RDA and Mantel analysis found that,SOC,total N,NAG,Mo,Cu,vegetation coverage,grass layer height,dominance were the main factors affecting bacterial communities.4)Based on the molecular network model,the altitude and aspect significantly affected the stability of the soil microbial community in the alpine meadow.With the increase in altitude,the looseness and instability of the molecular network model structure of fungi and bacteria were basically first increase and then decreases,the looseness and instability of the molecular network model structure in sunny aspects was higher than that in shady aspects.SOC,total N,available N,bulk density,Se,Co,and vegetation coverage were the main environmental factors affected the stability of the microbial network structure.The change of microbial community structure network was restricted by vegetation and soil factors in the habitat.5)In the process of alpine meadow vegetation changing with altitude and aspect orientation,soil bulk density,water content,SOC,total N,available P,Mo,Mn,C/N,N/ P,AP,PPO,urease.The soil bulk density,total P,Zn,soil water content,available K,POD,PPO were the main driving factors in the alpine meadow fungal community changing process with altitude and aspect.Water content,Cu,total N,SOC,Se,NAG,C/N,Sucrase,POD,and urease were the main driving factors of bacterial communities in alpine meadows.The evolution of alpine meadow vegetation with altitude and aspect direction significantly changed the composition of the fungal community and the diversity of the bacterial community.The results of the structural equation model show that,the evolution of the alpine meadow in the Qilian Mountains with altitude and aspect,the changes in soil microbial community structure were mainly affected by soil characteristics and vegetation characteristics.The cumulative contribution rates of vegetation and soil were 0.52 and 0.71,respectively.And soil has the greatest impact on soil microorganisms.Cluster analysis found that,the 3000 m and 3400 m altitude lines can be used as reference lines for the regional management of alpine meadow resources.In summary,the research found that,the evolution of altitude and aspect directly affected the distribution and composition of alpine meadow plants,while the changes in vegetation characteristics affected soil and microorganisms.Meanwhile,soil microbial communities reacted to the soil in order to adapt to changes in vegetation and soil,and further affecting the grassland vegetation.From the evolution of vegetation,soil and microorganisms as a system with altitude and aspect direction,the altitude of 3200 m was the central area of alpine meadows distribution in the Eastern Qilian Mountains,and the productivity was mainly limited by nitrogen,which the restrictions in high and low altitude areas were particularly prominent.The optimum ratio of the three phases of soil "solid-liquid-gas" should be close to 31:33:36.And the altitudes of 3000 m and 3400 m are the critical lines for changes in the vegetation,soil and microorganisms of the alpine meadow in this area.And ridges should be avoided as the management line for grassland boundaries,and slope differences should be considered.