Diversity and distribution of the microbiome in the bulbs and rhizosphere soil of Fritillaria thunbergii

As global medical resources become increasingly scarce, the demand for medicinal plants continues to rise. The growth and metabolism of medicinal plants are closely linked to rhizosphere and endophytic microorganisms. The rhizosphere soil and internal tissues of plants form stable, nutrient-rich ecosystems largely dominated by microbial communities. However, how the rhizosphere and endophytic microbiomes of Fritillaria thunbergii vary across geographically distinct populations, and what ecological processes shape their assembly and functional potential remain largely unexplored. We hypothesized that distinct environmental selection pressures and spatial isolation would differentially shape the assembly of bacterial and fungal communities in bulb and rhizosphere niches, and that core and unique microbial taxa play pivotal roles in shaping ecological network structure. In this study, metabarcoding was employed to investigate the bacterial and fungal communities in the rhizosphere soil and bulbs of F. thunbergii across four populations in China, with the aim of elucidating the biogeographic patterns, assembly mechanisms, and ecological networks of the plant-associated microbiome. The results indicate that both bacterial and fungal communities exhibited significant differences in diversity and composition across the four populations, shaped jointly by geographic isolation and environmental selection. Only a few taxa displayed both cosmopolitan distributions and high abundance, whereas most communities were distinct among ecotypes. Co-occurrence network analysis revealed that core taxa exerted stronger ecological relevance within bacterial and fungal communities compared to other ecotypes, while unique taxa played more pivotal roles in cross-domain networks. Phylogenetic analyses further uncovered microdiverse clades shaped by environmental selection, which may enhance functional resilience and contribute to the overall biogeographic patterns observed. By elucidating the biogeographic patterns and assembly mechanisms of the F. thunbergii microbiome, the study provides a conceptual framework for understanding plant-microbe interactions in medicinal plants and offers insights for the sustainable utilization of microbial resources in traditional medicine.