Rhizosphere bacterial community confers drought tolerance to Astragalus mongholicus

Drought stress significantly inhibits the growth of Astragalus mongholicus, leading to reduced biomass, decreased photosynthetic efficiency, and exacerbated oxidative damage. In our study, the accumulation of saponins and flavonoids in Astragalus roots markedly increased under moderate drought stress. These secondary metabolites further reshaped the rhizosphere microbial community structure, significantly increasing its diversity and interaction network complexity. Notably, drought stress enriched beneficial bacterial genera such as Rhizobium and Pseudomonas in the rhizosphere soil. Combined with the isolation of culturable microorganisms and the co-occurrence network of the rhizosphere bacterial community, we constructed a 13-strain synthetic community (SynCom) and simplified it to 7 strains. Compared with the noninoculated control, under moderate drought stress, inoculation with the simplified SynCom significantly increased plant growth, increasing the aboveground fresh weight by 50.10 %, dry weight by 55.29 %, and underground fresh weight by 76.40 %. Similarly, plants treated with the synthetic community presented significant increases in aboveground fresh weight and dry weight compared with those of the noninoculated control, with increases of 46.98 % and 61.54 %, respectively. Moreover, inoculation with the simplified community significantly reduced the content of malondialdehyde (MDA) and improved the catalase (CAT) and peroxidase (POD) activities and leaf photosynthetic parameters (Fv/Fm and Y(II)) of Astragalus. Our findings provide new insight into improving the yield and quality of Astragalus and highlight the potential of synthetic rhizosphere microbial communities for assisting plants in coping with abiotic stress.