Rhizosphere bacterial and fungal spatial distribution and network pattern of Astragalus mongholicus in representative planting sites differ the bulk soil

Abstract

The soil microbiome is a crucial component of earth ecosystems and plays an important role in cycling nutrient elements and sustaining plant growth. The spatial distribution of the microbial community in the bulk soil and rhizosphere of crops has been well studied; however, the biogeographic patterns of the microbial community in medicinal herbs are poorly understood. Here, we compared the biogeographic patterns and assemblages of bacterial and fungal communities in the bulk soil and rhizosphere from 152 samples in three representative Astragalus membranaceus Bges. var. mongholicus (Bge.) planting sites. Additionally, the contents of bioactive ingredients in plant roots were determined by liquid chromatography-mass spectrometry (LC-MS). The results showed that the bacterial and fungal composition and diversity differed between the bulk soil and rhizosphere soil at different sites. Redundancy analysis (RDA) combined with multiple regression on distance matrices (MRM) and Mantel tests indicated that pH and available potassium (AK) were the predominant factors affecting the bacterial and fungal communities in the bulk soil, respectively, while total phosphorus (TP) and total nitrogen (TN) were the dominant factors correlated with the bacterial and fungal communities in the rhizosphere. The rhizosphere networks had fewer nodes and edges, a lower density, and a lower average degree but higher modularity and greater positive links than the bulk soil networks, suggesting that a less complex topology and niche sharing were features of the A. mongholicus rhizosphere network. The distance-decay pattern showed that the bacterial and fungal communities in the bulk soil and rhizosphere displayed somewhat similar dissimilarity. Stochastic processes mainly shaped the microbial community structures in both compartments. Finally, we found that the contents of bioactive ingredients in plant roots were distinct and associated with the fungal microbiome. Taken together, our results revealed that the spatial distribution and network pattern of bacterial and fungal communities in the A. mongholicus bulk soil and rhizosphere were distinct, which could help elucidate the rhizospheric microbiome assemblage of medicinal herbs and provide production strategies for A. mongholicus.