Diversity Patterns Of Microbial Communities Of Endophyte,Root Zone Of Bothriochloa Ischaemum,and Soils On Dam Of Copper Mine Tailings

Understanding the biodiversity distribution patterns and community assembly mechanisms have long been a central aim in ecological research.At present,although some hypotheses about community assembly were reported,universality was still controversial.Traditionally,the diversity,structure and composition of natural communities were explained through‘niche-based'mechanisms.However,Hubbell et al.assumed that stochastic processes or dispersal limitation is the primary of determinants.The debates were reconciled by Gravel et al.to that niche control and neutrality are the opposite ends of a continuum,and most natural communities lie somewhere between these theoretical extremes.That is,the two processes work together.Many investigations have been conducted to reveal the factors,such as type or traits of organisms,research scale,habitat,that determine the position of natural communities on this continuum.We selected the Shibahe copper tailings dam located in Yuanqu County of Shanxi Province as the research sample.In order to reveal the mechanisms and relationships of different microbial community diversities under heavy metal stress,the endophyte,root zone?including the Rhizosphere and non-rhizosphere?and non-root zone soil microbe of Bothriochloa ischaemum at tailing dams have been selected as the research objects.Based on the results of 16S rDNA and 18S rDNA denaturing gradient gel electrophoresis?DGGE?,we analyzed the diversity of endophyte and the rDNA-ITS phylogenetic analysis,and then analyzed the structure and diversityof endophyte,rhizosphere,non-rhizosphere and soil microorganisms community.The correlation analysis,mantel test,structural equation model,variance decomposition and null model were used to analyze the environmental and spatial factors that affect the structure and diversity of microbial community.Then we discussed the relative role of the neutral processes?stochastic processes?and niche processes?deterministic processes?in microbial community assemble.The research showed the following conclusions:1.Distribution and rDNA-ITS sequence analysis of endophyte symbiosis with B.ischaemum in copper tailings?1?Twenty-one kinds of endophyte were isolated from the Bothriochloa ischaemum of 6 different restoration years by PDA medium separation.The colonies differed in morphology with growth rates ranging from 8.248 to87.638 mm/week.The spore morphology was mainly spherical and oval with spore sizes ranging from 0.682 to 7.072?m.?2?The results of molecular identification showed that there were 8types of 5.8S-ITS sequences of 21 endophyte belonging to Fusarium,Gibberella,Penicillium,Septoria,Irpex and Sphaerotheca.The results of genetic distance analysis showed that genetic distance of endophytic fungi of B.ischaemum between sub-dams with different restoration ages was different?0⁰.985?.?3?Phylogenetic analysis between endophyte from B.ischaemum and known endophyte that adsorbing heavy metals showed that I21 had a relatively close genetic relationship with Trichoderma viride.I20 and Trametes versicolor have a closer relationship.?4?Meanwhile,the environmental distances caused by different restoration years had effects on the genetic distance and Jaccard dissimilarity coefficient of endophyte between sub-dams.Space factors had no influence on genetic distance and diversity.This suggested that the diversity of endophyte in the copper tailings was driven by environmental selection.2.The diversities and structures of microbial community in rhizosphere,non-rhizosphere and non-root zone soil in copper tailings.?1?Correlation analysis showed that the amount and?-diversity of rhizosphere and non-root zone microorganisms were the most affected by NH₄⁺-N,TN,TC and pH.Furthermore,the diversity and amount of non-rhizosphere and rhizosphere fungi were also affected by the grain size and plant height.?2?Bacterial and fungal community structures are mainly affected by emvironment.Structural equation model analysis found that microbial community structures were affected by vegetation,including vegetation diversity and plant height expect to non-rooted soil and non-rhizospheric fungi.Soil nutrients and heavy metals had a greater impact on non-root soil fungi,and had little effect on bacterial community structure.?3?Null model analyzed showed that the rhizosphere,non-rhizosphere and soil microbial communities were all greatly affected by the niche processes.Rhizosphere soil bacteria?null deviation=-0.248±0.023?,non-rhizospheric soil bacteria?null deviation=-0.234±0.037?and non-root zone soil bacteria?null deviation=-0.242±0.030?were the most affected by the deterministic process,followed by rhizosphere soil fungi?null deviation=-0.161±0.024?andnon-rhizosphericsoilfungi?null deviation=-0.168±0.030?,non-rootzonesoilfungi?null deviation=-0.141±0.023?were the least affected by deterministic processes.Deterministic processes had a greater effect on bacteria than fungi,supported the"Size-dispersal"hypothesis.In conclusion,the assembly of endophyte,rhizosphere and non-rhizosphere soil microorganisms and non-root zone soil microbial communities in heavy metal pollution area at local scale were all contributed by deterministic process mostly,that is to say environmental selection.