The Elevational Distribution Patterns Of Soil Microbial Community In Alpine Meadow

Soil microorganisms as the major decomposers,are essential members in terrestrial ecosystems.They are playing important roles in mediating biogeochemical processes,such as carbon,nitrogen cycling and maintaining the functions of ecosystem.Soil microorganisms could easily be affected by the changes of environmental factors,such as soil environment,plant communities and climate changes,and could be used as an indicator of environmental change of local ecosystem.With the rapid development of molecular technology,researchers began to study the structure and function of microbial community at gene level.Sanjingyuan,known as “Chinese water tower”,is located in the hinterland of Qinghai-Tibet Plateau.The unique natural geographical location and ecological environment of Sanjiangyuan have bred abundant species resources and special ecosystems.The alpine meadow,widely distributed in the regions of 3000 m above sea level,is considered to be one of the most important and representative vegetation types in Sanjiangyuan.However,with the global climate change and human activity,the alpine meadow of Sanjiangyuan is facing great changes,such as degradation or evolution.This phenomenon would bring about a huge impact to biological diveristy and ecological functions of Sanjiangyuan.Studying the characteristics of microbial community along the elevation in alpine meadow of Sanjiangyuan,would provide valuable information for predicting the global changes and revealing the special microbial flora of unique geography environment.In our study,the metagenomics technology and conventional microbiological detection technology were used to study the distribution of microbial community along the elevation of3220—4790m in Sanjiangyuan Natural Reserve.And we further anlysed the internal influential mechanism that shaping the elevational distribution of soil microbes.In addition,we detected the response of soil microbial community to the evolution of alpine meadow which was vulnerable impacted by global changes.The main conclusions were as the following:(1)By using Illumina high-throughput sequencing technology,we analysed the elevational patterns(3220-4790)of soil microbial community structure,and further analysed the major environmental factors that impacted microbial distribution.The results indicated that the dominant phylum across all samples were Proteobacteria,Acidobacteria and Actinobacteria,and accounted for more than 70% relative of the abundance,indicating that these three phyla were most important bacteria groups in alpine region.There was significant(P < 0.05)difference of microbial communities among the six sites,according to detrended correspondence analysis(DCA)and several dissimilarity tests(MRPP,Anosim and Adonis).And the relative abundance of all detected kinds of phylum had different changing tendency along the elevation.Through analysis microbial ?-diversity of six sites,the richness of OTUs ranged from 3784.92±537.45 to 4193.00±434.00 and the Shannon index ranged from7.37±0.19 to 7.53±0.14,while the Simpson index ranged from 608.10±143.45 to801.12±104.12.Through analyze the varying trend of these three indexes along elevation,the pattern of microbial diversity along the elevational gradient is not obvious.Analyzing the envrionemental factors to microbial communities based on Mantel test,we observed that pH was a better predictor in shaping soil microbial community elevational distribution.What's more,soil moisture,soil organic carbon and soil available nitrogen were also important driving factors in affacing microbial communities along the elevational gradient.(2)Actinobacteria are important environmental microbial groups and they are widely distributed in all kinds of ecological environments.Strengthening the understanding to the structure and distribution of Actinobacteria has important implications for protecting the resource of Actinobacteria.In our study,a total of 5057 OTUs were detected,which could attributed to 230 genera,52 families,9 orders and 5 subclasses of Actinobacteria,and the Actinobacterial communities were significantly(P < 0.05)different among the six sites,according to DCA and dissimilarity tests(MRPP,Anosim and Adonis).The subclasses of Actinobacteridae and Rubrobacteridae were dominant in all six sites,and accounted for more than 80% relative of the abundances,indicating that Actinobacteridae and Rubrobacteridae were the most important subclasses in the high elevational grasslands.Through analysis ofActinobacterial ?-diversity of the six samples,the number of OTUs ranged from 447.23±52.83 to 675.00±114.69,and the Shannon index ranged from 5.35±0.15 to 5.78±0.11.Both of the measures exhibited strong negative(P < 0.01)correlations with the elevational gradient,indicating that the environmental conditions of higher altitude may not benefit to the survival of Actinobacterial species.Mantel test was implemented to identify the major environmental factors that impact Actinobacterial communities.The result indicated that soil temperature,moisture,organic carbon and nitrogen contents were significantly(P < 0.05)correlated with Actinobacterial community structure and they could be the important factors in determining the distribution of soil Actinobacteriain the grasslands of the Tibetan Plateau.(3)Based on Illumina high-throughput sequencing technology,Biolog micro-plate and Geochip-based metagenomic technology,we analyzed the probably changes of soil micoribal communities with the evolvement happening from alpine meadow to alpine steppe meadow,and we wanted to reveal the ecological mechanism in functional level with the phenomenon occur.The studying results indicated that microbial community structure in the two meadow type was significatly differed(P < 0.01)according to DCA and dissimilarity tests(MRPP,Anosim and Adonis),and microbial ?-diversity in alpine medow was significantly(P < 0.01)lower than that of alpine steppe meadow.In order to detect the interactions among different microbial communities,we constructed the correlated ecological network based on a random matrix theory(MRT).The result indicated that the ecological network of microbial community structure in alpine steppe meadow was more complex and tighter than that of alpine meadow,implicating microbial community stucture and their interactions would be changed with evolvement occuring.Functional genes and biolog carbon substrate utilization analysis showed that microorganisms in alpine steppe meadow may decompose and utilize more organic carbon than alpine meadow.With alpine meadow disappearing,much carbon stored in soil would be released as the form of CO2.This phenomenon would not conducive to store soil organic carbon.The Mantel test,CCA and VPA analysis were used to determine the key environmental factors that impact soil microbial community in the process of alpine meadow evolution,andthe result indicated that vegetation property,soil organic carbon and soil phosphorus were the crucial factors in impacting microbial community.