Community Assembly and Functional Analysis of Rhizosphere Rare Bacteria in Daodi Angelica sinensis

Objective To analyze the diversity characteristics of rhizosphere bacteria of different ecotypes (wild, semi-wild and cultivated type) of Angelica sinensis in authentic producing areas, and to clarify the community assembly mechanisms and functional differentiation rules of abundant and rare bacteria.

Method Based on 16S rRNA gene amplicon sequencing technology, the structure and function of the rhizosphere bacterial community of A. sinensis were analyzed. Functional and phenotypic predictions were performed using PICRUSt and BugBase software. The null model was used to quantify the contribution of deterministic/stochastic processes to the assembly of rare and abundant bacteria.

Result The rhizosphere bacterial community of A. sinensis consists of abundant species with extremely low abundance (0.067%) and rare species with high abundance (49.73%). The Shannon index and Chao1 index of rare bacteria were significantly higher than those of abundant bacteria, and their community structure and assembly process were more complex. The species composition showed that rare bacteria were mainly composed of Firmicutes, Proteobacteria, Acidobacteriota, Myxococcota, Planctomycetota, Bdellovibrionota, Patescibacteria, and Chloroflexi, while abundant bacteria were composed of Actinobacteriota and Proteobacteria. Differential species analysis indicated that Arthrobacter and Paenibacillus were the significantly differential species in cultivated A. sinensis (Z); Haliangium, Bradyrhizobium, Microlunatus, Mycobacterium, and Mesorhizobium were the significantly differential species in wild A. sinensis (Y); Rhodococcus and Aquicella were the significantly differential species in semi-wild A. sinensis (YZ). The community assembly mechanism revealed that stochastic processes, dominated by drift (40.74%-62.00%) and supplemented by dispersal limitation (14.00%-30.00%), drove the community assembly of rare rhizosphere bacteria of A. sinensis, while stochastic processes dominated by dispersal limitation (72.00%-88.00%) and supplemented by drift (10.00%-13.58%) drove the assembly of abundant bacteria. Functional prediction showed that abundant and rare bacteria had functional dominance and phenotypic complementation effect. The functional abundance of KEGG level 1 in abundant bacteria increased with the domestication gradient, while rare bacteria showed a downward trend. The functional abundance of abundant bacteria was 25-76 times that of rare bacteria.

Conclusion The rhizosphere bacterial community of A. sinensis is composed of a small number of abundant species and a large number of rare species. Both are driven by stochastic processes, but show significant differentiation in composition structure, assembly mechanism, and functional contribution.