Microbial Diversity In The Ectomycorrhizal Rhizosphere Soil Of Castanopsis Hystrix

Microbial communities play a key role in ecosystem function,but our understanding about the determinants of their diversity and biogeographic patterns in plant roots and soils is limited.Castanopsis hystrix is a kind of native broad-leaved timber species widely distributed in subtropical areas of China,and it is a typical ectomycorrhizal nutritional tree species.To understand the microbial diversity and community structure in multiple underground habitats of C.hystrix,Guangdong and Guangxi were selected as the study areas to collect ectomycorrhiza(EM),rhizosphere soil(RS)and bulk soil(BS).Using the Illumina Mi Seq high-throughput sequencing to analyze the microbial diversity and community composition in the three habitats,and the symbiotic fungi and bacteria were screened out to reveal the composition and co-occurrence of EM fungi and mycorrhiza helper bacteria associated with C.hystrix,which provided an ideal microflora combination for the research and development of compound microbial agents.Moreover,combined with soil physicochemical properties to clarify the key driving factors affecting microbial community characteristics.The main research results were as follows:(1)High-throughput sequencing was used to characterize microbial communities across the three habitats(i.e.,EM,RS,BS)and found significant differences in both bacterial and fungal community composition.EM and soil presented different microbial habitats with specific sets of microbes.EM fungal communities were similar to each other and to soils,with communities being dominated by Basidiomycota(Agaricomycetes)and Alphaproteobacteria.Basidiomycota was associated with a large number of EMF.The soil was also dominated by these groups,but rich in Acidobacteria,Mortierellomycota,Ascomycota(Eurotiomycetes)and Actinobacteria.As a medium connecting soil and plants,the rhizosphere contains more abundant biological species,and the research found that richness and diversity of microbial communities in the RS were higher than those in the EM and BS.(2)The results suggested that RS were more nutrient-rich compared with BS.Of all the measured soil physicochemical properties,soil organic matter,total nitrogen,available phosphorus and available potassium contents in RS were significantly higher than those in BS,while the p H was slightly higher than that in RS.Correlation analysis between mycorrhizal colonization and soil physicochemical parameters showed that mycorrhizal colonization was significantly positively correlated with soil p H,total nitrogen,total phosphorus and available potassium contents.Redundancy analysis showed that soil p H was the strongest driving factor affecting microbial community composition.(3)Bacterial functional groups were affected by microbial habitats,the abundance of bacteria with nitrogen fixing and nitrate reducing in EM was significantly higher than that in soil.Nitrogen-fixing bacteria were the most abundant in EM of C.hystrix and Pinus massoniana mixed plantation.PICRUST analysis showed that membrane transport pathways and signaling molecules and interaction pathways,including ABC transporters,transporters,PTS,Cam Ligands,ECM-receptor interaction and neuroactive were more abundant in EM than that in soil.(4)The composition of EMF community associated with C.hystrix was relatively rich.A total of 427 EMF OTU associated with C.hystrix were screened,belonging to 27 genera,and Basidiomycetes were the dominant.The dominant genera were species of Russula,Clavulina,Sebacina,Helvellosebacina,Lactarius,Inocybe,Laccaria,Tomentella,Boletus,Scleroderma and Amanita.Among them,Russula was the predominant group.The relative abundance of EMF in the EM was higher than that in RS,but the symbiotic fungi were more abundant than that in EM.Most of the symbiotic fungi in EM were from soil,and all 13 EMF genera in EM were shared with the rhizosphere symbiotic fungal community.(5)There were more than 10 genera of mycorrhiza helper bacteria in mycorrhizosphere of C.hystrix,including Burkholderia,Pseudomonas,Bradyrhizobium,Azospirillum,Rhizobium and Bacillus were dominant genera.The relative abundance of MHB in the EM was higher than that in the RS.(6)The C.hystrix and P.massoniana mixed plantation could significantly promote the colonization of Russula and MHB in the roots of C.hystrix.Moreover,soil p H,available potassium,total phosphorus,and total nitrogen which were positively correlated with mycorrhizal colonization were significantly higher than those in other plots.These factors promoted the formation of EM,resulting in high colonization rate in the forest.