Patterns And Mechanisms Of Microbial Diversity Along A Precipitation Gradient On The Tibetan Plateau

Microorganism is an indispensable part of the ecosystem and participates in many important ecological processes.Current researches on the diversity and composition of microorganism have been relatively sufficient.Compared with the biogeographical patterns of animals and plants,the microbial geography is an emerging field.Most current studies focus on the elevational and latitudinal gradients of microbial diversity,and less attention has been paid to the patterns of microbial diversity along a precipitation gradient,and the mechanisms behind these patterns are still unclear.By exploring diversity patterns of soil bacteria and fungi along the precipitation gradient on the Tibetan Plateau and combining with the analysis framework of threedimensional diversity(α、β,and γ diversity),this paper hopes to provide a new method for revealing the mechanisms behind biogeographical patterns of soil microbes.In this study,a horizontal transect with a precipitation gradient on the Tibetan Plateau was selected with a nested sampling design.During 2019 to 2020,we selected 55 sites and set a quadrat every 20 m in each site along the transect.There were 275 quadrats in total.We collected soil samples and conducted plant community surveys at each quadrat.α-diversity was measured as the number of species within the quadrat,β-diversity was measured as the community difference between quadrats,and γ-diversity was measured as the total number of species within the site.We obtained the patterns of microbial and plant diversity along the precipitation gradient,combined with environmental data of precipitation,temperature,longitude,latitude and altitude,and tried to reveal the mechanism behind microbial diversity patterns.The study found: 1)The large-scale diversity patterns along the precipitation gradient(γ-diversity)of bacteria and fungi were consistent,both bacterial and fungal γ-diversity decreased with the decreasing precipitation.However,while splitting γ-diversity into α-diversity and β-diversity,we found that the decrease of bacterial γ-diversity was caused by the decrease of β-diversity,which was mainly due to biological homogenization;the decrease of fungal γ-diversity was caused by the decrease of α-diversity,which was mainly due to systematic decline of fungal diversity in each quadrat.2)The factors which affected different dimensions of diversity were slightly different.Both α-diversity and β-diversity of bacteria were mainly affected by precipitation.Fungal β-diversity was mainly affected by precipitation as well,while fungal α-diversity was mainly affected by plant α-diversity.3)Precipitation affected bacterial and fungal γ-diversity through different ways.Precipitation did not affect bacterial α-diversity,but indirectly decreased bacterial β-diversity through decreasing plant β-diversity,finally forming the pattern that bacterial γ-diversity decreased with precipitation.Further,precipitation decreased fungal α-diversity through decreasing plant α-diversity,finally forming the pattern that fungal γ-diversity decreased with precipitation.In summary,we found patterns of bacterial and fungal γ-diversity were consistent along the precipitation gradient.However,by applying the analytical framework of the three dimensions of α,β,and γ diversity,we found that mechanisms behind the diversity patterns of bacteria and fungi were different.Such a method may help us to reveal the mechanisms behind the patterns.