Biogeographical Patterns And Mechanisms Of Forest Soil Microbial Community Along An Elevation Gradient In Shennongjia National Nature Reserve

Biogeographic patterns and mechanisms of soil microbial communities have solicited much attention due to the central role of microbes in biogeochemical cycles.The development of microbial geography was relatively backward compared to macroorganisms due to the technological limitation.Recent advances in our ability to quantify microbial community composition in natural habitats have prompted new campaigns to explore microbial world,which enables the understanding of microbial biogeography not only of taxa but also of functional traits.It has been proved that soil microbial community truly exhibited biogeographic patterns but not simply “everything is everywhere”.Shennongjia national natural reserve(SNNR),located in Northwest Hubei province of China,is one of the most biologically diverse areas in China and a member of UNESCO's World Network of Biosphere Reserves,and is often known as “The Oriental Botanic Garden” and the natural bank of biological species.Here we characterized soil microbial communities with 16 S rRNA gene-based sequencing and a microarray named Geo Chip 4.0 to determine how microbial community taxonomic and functional traits varied along the elevation gradient.We found that:(1)The biogeographic patterns and mechanisms of microbial taxonomic structure and functional structure were different.The microbial taxonomic structure was significantly divergent along the elevation gradient,with few ubiquitously distributed microbes,which fitted the neutral theory and was best explained by dispersal limitation.By contrast,functional structure was highly convergent,with most functional genes ubiquitously distributed,which fitted the niche-based theory,and correlated with soil geochemical traits.(2)The control factor of microbial community was varied under different research scales.Along the elevation gradient,dispersal limitation was the most important factor in shaping microbial taxonomic structure,while soil geochemical traits were shaping microbial functional structure.Within local scale,temperature was the best predictor for microbial community variations in the timberline,while soil organic matter quantity and quality was the best predictor of microbial community in the broadleaf forest.(3)The relationship of microbial structure and function was varied with different microbial groups.There is a lack of taxonomic-functional relationship for soil microbial communities along the elevation,which suggests a high degree of functional redundancy among whole microbial communities.However,the ammonium oxidizer was positively correlated with bacterial amoA gene abundance in timberland,indicating a low degree of functional redundancy among this narrow group of ammonium-oxidizing mediator.(4)Microbial functional structure could serve as an indicator of soil environment.The microbial functional composition was better correlated to soil geochemical parameters along the elevation gradient.Furthermore,the abundances of nitrogen cycle in timberland were concomitant with NH4+-N and NO3--N,and the recalcitrant carbon degradation genes were concomitant with the organic accumulation in broadleaf forest.All these indicated a function-based approach might be better to understand the importance of microbial traits in a specific habitat.