Study On Bacterial Diversity Of Rhizosphere Soil Of Six Species Of Astragalus In Qinghai-Tibet Plateau

Astragalus plants are widely distributed in the Qinghai-Tibet Plateau,and some of its species are regarded as indicators of grassland degradation and are called loco-weeds.In this study,six species of Astragalus in the Qinghai-Tibet Plateau,Astragalus heydei Baker,Astragalus arnoldii,Astragalus densiflorus,Astragalus yunnanensis,Astragalus strictus and Astragalus confertus,as the research objects,used pure culture methods and high-throughput sequencing technology to conduct experimental research to analyze six species of Astragalus plant rhizosphere soil bacteria Diversity,structure and function,and their relationship with environmental factors.The characteristics of the rhizosphere bacteria of two grassland degradation indicator species,Astragalus strictus and Astragalus arnoldii,were further analyzed,and the relevant results are as follows:Using traditional LB medium to separate and purify bacteria,a total of 46 strains of bacteria were obtained.The bacteria were identified by 16 S rRNA sequence analysis.A total of 23 species were classified into 9 genera.namely Arthrobacter,Paenibacillus,Exiguobacterium,Lysinibacillus,Enterobacter,Planomicrobium,Stenotrophomonas,Pseudomonas and Bacillus.A phylogenetic tree was established based on the results of 16 S rRNA sequencing,It forms four large branches.Bacillus was found in the rhizosphere soil samples of six species of astragalus.Through 16 S rRNA high-throughput sequencing,2022565 effective sequences were obtained.These sequences were annotated as 1882 OTU,and 572 genera in 32 phyla were annotated in total.The Sobs richness index of each sample has extremely high and significant differences.Shannon diversity index showed that bacterial diversity in rhizosphere soil of astragalus straight and Astragalus arnoldii matted was significantly higher.and the community diversity of the rhizosphere soil bacteria of the six Astragalus species There are obvious differences,Alpha diversity analysis showed that,the order of diversity is Astragalus strictus>Astragalus arnoldii>Astragalus yunnanensis>Astragalus densiflorus>Astragalus confertus>Astragalus heydei Baker.The results showed that the two grassland degradation indicator species of Astragalus strictus and Astragalus arnoldiihave high bacterial diversity in the rhizosphere soil.The community structure is stable,which is not conducive to grassland degradation management.PCo A analysis showed that Astragalus densiflorus and Astragalus arnoldii had a high similarity,and Astragalus strictus had a good similarity with clustered Astragalus confertus.The difference between Astragalus yunnanensis groups was the smallest.Community composition analysis and difference analysis showed that the dominant phyla in the rhizosphere soil samples of six species of astragalus plants were distributed in 45 gene of 7 phyla.and the core bacteria phyla were distributed in three phyla of Proteobacteria,Firmicutes and Actinomycetes,Which is consistent with the research results of Arabidopsis and other rhizosphere bacteria.Among them,Rhodococcus,Serratia,Pseudomonas,Kluyvera,Lachnoclostridium?5,etc.,are the five with the highest proportion Dominant bacteria.Kruskal-Wallis rank-sum test analysis at the genus level found that all samples have significant differences in Rhodococcus,Serratia,Kluyvera,Enterobacteriaceae,and Clostridium?sensu?stricto?1(0.01<P?0.05),in Hafnia,Proteus,Clostridiaceae?1 and Clostridium?sensu?stricto?12 have extremely significant differences(0.001<P?0.01).The species with significant differences in bacteria at the phylum level are Deinococcus-Thermus,Planctomycetes,Gemmatimonadetes,Saccharibacteria,Actinomycetes Actinobacteria,TM6(Bacillus cereus),SHA?109,Verrucomicrobia,Chlorofexi,Chlorobi,Acidobacteria,Nitospirae.Co-occurrence network analysis showed that Lachnoclostridium?5(17.23%),Serratia(12.14%)and Clostridium?sensu?stricto?1(40.08%)are closely related and exist in six samples.A variety of environmental factors have important effects on plant rhizosphere bacteria.The bacterial community in rhizosphere soil of Astragalus plants is related to environmental factors.Heatmap analysis shows that the order of the influence of soil physical and chemical factors on plant rhizosphere bacteria is: AP>AK>OM>AN>DT,and they are all negatively correlated.Available phosphorus,available potassium,organic matter,ammonium nitrogen and dew point had negative correlation on the flora structure.Function prediction analysis showed that the abundance of unknown functional gene families was the largest in the six samples,indicating that the potential functional genes of the flora in all samples were very abundant.The core flora of bacteria is: Pseudomonas,Gaielales,Gemmatimonadaceae and other bacterial genera.In summary,this study revealed the changes in the bacterial diversity and structural functions of the rhizosphere soil of six Astragalus species on the Qinghai-Tibet Plateau.The expression of core flora and functional genes was stable,and the spatial variation of bacterial diversity had different driving factors.Driven by a variety of environmental factors.Environmental factors have a significant impact on the structure of the flora and the dominant bacterial genera.The function prediction analysis shows that the abundance of each functional gene in different regions is similar.Genes related to the biosynthesis and catabolism of secondary metabolites provide the possibility for other metabolic pathways and biological functions to play a role.It provides a possible way for the biological management of grassland degradation indicator species of Astragalus,but its internal signal transduction mechanism needs to be further studied and verified.