Characterization of root microbial communities associated with Astragalus membranaceus and their correlation with soil environmental factors

The study aims to explore the structure of rhizosphere and root endophyte microbial communities of Astragalus membranaceus and the correlation among various soil environmental factors. The root-related microbial communities of A. membranaceus at four sampling sites in Dingxi City (i.e. Longxi, Minxian, Weiyuan and Zhangxian), Gansu Province, were studied by high-throughput sequencing technology. 1676 bacterial OTUs and 1718 fungal OTUs were obtained from rhizospheric soil samples, respectively. On the other hand, 1769 bacterial OTUs and 214 fungal OTUs were calculated from root endophyte samples, respectively. The predominant species inside the root of A. membranaceus were confirmed to be Proteobacteria, Bacteroidete and Acidobacteria at bacterial phylum level, and Ascomycota and Mortierellomycota at fungal phylum level, respectively. PCoA and NMDS analyses demonstrated that the microbial community composition of rhizosphere was significantly different from that of endophyte, especially the rhizospheric bacteria and endophytic fungi of A. membranaceus in Longxi region, which were distinguished from other regions. The results of co-occurrence network analysis showed that the network structure of rhizosphere microorganisms was more complex than that of root endophyte, and the network interaction among distinct bacteria was closer than that of fungi. Moreover, RDA analysis illustrated that Proteobacteria possessed strongly positive associations with TN and AN, and Ascomycota was strongly positively associated with pH and PRO. Mortierellomycota was in high abundance within A. membranaceus endophyte in Longxi region and was negatively correlated with SOM. AN inflicted the greatest effect on the root microbial community. Taken together, we provide powerful evidence that A. membranaceus has abundant microbial community, whose composition and diversity are influenced by various soil environmental factors.