Biogeographical Patterns And Driving Mechanisms Of Phyllosphere Microorganism

As an important part of the plant microbiome,microbes in phyllosphere play vital roles in the ecosystem,with ecological functions such as improving the host plant disease resistance,producing hormones to promote plant growth,degrading contaminated organic matter such as pesticides,and participating in the global biogeochemical carbon and nitrogen cycling.The study of microbial biogeographical distribution patterns is helpful to understand the mechanism of microbial diversity generation and maintenance.However,the microbial biogeographical distribution pattern and its driving mechanism of the phyllosphere microorganism are still unclear.The eastern part of China is characterized by natural hydrothermal gradient,diversity of ecosystem types and diversity of management methods,which is an ideal platform to study the distribution pattern of microbial biogeography.Therefore,the research on the geographic distribution pattern and its driving mechanism of the phyllosphere microbial community in eastern China is helpful to understand the generation and maintenance mechanism of the phyllosphere microbial diversity,and provide a theoretical basis for the development of sustainable agriculture.In this study,343 foliar samples were collected from seven ecosystem types in eastern China.Using high-throughput sequencing technology,we explored the differences in the geographic distribution patterns of phyllosphere microbiome communities between anthropogenic and natural ecosystems,and revealed the assembly of phyllosphere microbiome community.Moreover,the biogeographic distribution pattern and driving mechanism of the core and rare taxa were explored,and the main ecological functions of the phyllosphere microorganism community were predicted.The main results are as follows:1)The differences in the composition and biogeographical distribution pattern of phyllosphere microbial communities between anthropogenic ecosystem and natural ecosystem were compared.The results showed that there were significant differences in the phyllosphere microbial community structure between the anthropogenic ecosystem(paddy ecosystem,upland ecosystem,polytunnel ecosystem,urban area ecosystem)and the natural ecosystem(grassland ecosystem,forest ecosystem,wetland ecosystem).Compared with the significant differences in the leaf microbial community structure of the anthropogenic ecosystem,There was no significant difference in the microbial community structure of natural ecosystem leaves.At the continental scale,the richness and phylogenetic diversity index of the phyllosphere microbial community in the anthropogenic ecosystem showed a significant monotonic decreasing relationship with latitude,while the latitudinal distribution pattern of the phyllosphere microbial community in natural ecosystem was not detected.There was a negative effect between the similarity of phyllosphere microbial community and geographical distance in anthropogenic ecosystem,while there was no significant correlation between the similarity of anthropogenic microbial community and geographical distance in natural ecosystem.2)Multiple regression linear model and null model were used to explore the mechanism and environmental driving factors of phyllosphere microbial community construction in different ecosystems.The results showed that the structure mechanism of phyllosphere microbial community in different ecosystems had similar rules.The stochastic process was dominant in the spatial variation of phyllosphere microbial community,which was mainly determined by homogenizing dispersal,and explanatory degree was more than 50%in different ecosystems.Variable selection in the deterministic process explained 19%-49%of the spatial variation of the phyllosphere microbial community.In addition,dispersal limitation and undetermined processes only account for about 10%of the spatial variation in phyllosphere microbial community composition.The results of multiple regression model further showed that annual mean temperature(MAT)and nitrate nitrogen(NO₃^--N)might be the main environmental factors controlling the variation of phyllosphere microbial community,and spatial distance had little contribution to the variation.3)Abundance-occupancy relationships were used to define core taxa on phyllosphere in different ecosystems.Although there is a high diversity of phyllosphere microorganisms,a continental scale core bacterial community consists of only 31operational taxonomic units,mainly including Pantoea(12.53%),Enterobacter(6.57%),Methylobacterium(5.41%),Sphingomonas(3.7%),Arthrobacter(3.44%),Pseudomonas(2.66%)and Curtobacterium(2.30%).In conclusion,agricultural management and human activities affect the geographic distribution pattern of phyllosphere microbial communities.Although the spatial turnover of phyllosphere microbial communities is largely driven by random processes,annual mean temperature and atmospheric nitrogen deposition are also important driving factors.At the continental scale,there is a core microbiota consisting of 31 OTU in the phyllosphere which shows high activity in metabolic processes such as carbohydrate.The results of this study provide theoretical data for human disturbance of ecosystem function and stable regulation,which will be helpful to maximize the ecological function of foliar microorganisms and promote the healthy growth of plants in future sustainable agriculture.