Transplantation-Driven Microbial Shifts and Keystone Taxa Enhance Medicinal Ingredients in Astragalus mongholicus

Root-associated microbes play a crucial role in plant growth, stress resistance and the accumulation of secondary metabolites. In this study, LC-MS analysis revealed that soil provenance exerts a decisive influence on the content of flavonoids and astragalosides in Astragalus membranaceus. Transplant assays revealed that each soil type acted as a selective filter, assembling distinct microbial communities in both the rhizosphere and root of Astragalus membranaceus. The rhizosphere taxa selected from Yangling soil specifically enhanced flavonoid levels, whereas the root taxa selected from TanChang soil drove higher astragaloside accumulation. SourceTracker revealed that seedling root-endosphere ASVs served as the primary inoculum for later communities, confirming strong priority effects among early colonizers. Keystones tightly linked to both metabolite contents and biomass belonging to Caulobacteraceae, Acidimicrobiia, Sutterellaceae, Bradyrhizobium, Sphingomonas and Mesorhizobium were isolated, and the SynComs were constructed. In Tanchang soil, SynComs inoculation raised Astragaloside IV (AST IV) and Calycosin-7-glucoside (CAG) contents by 52.30% and 55.73%, respectively; in Yangling soil, the same consortium increased Astragaloside I (AST I), Astragaloside II (AST II), AST IV and CAG by 29.38%, 39.04%, 54.97% and 58.98% compared to the uninoculated controls. Collectively, our work charts the transplantation-driven dynamics of root-associated bacterial communities and medicinal metabolites, pinpoints keystones that govern ingredient accumulation and delivers validated microbial strains for enhancing the quality and pharmaceutical value of Astragalus mongholicus.