Distinct large-scale biogeographic patterns of fungal communities in bulk soil and soybean rhizosphere in China

Fungi play a crucial role in the agroecological system; however, little is known about their large-scale biogeographical patterns and how various ecological processes contribute to community assembly, especially in the crop rhizosphere. In this study, we investigated the spatial distribution and community assembly of fungi in the bulk soil and rhizosphere of soybean collected from 43 sites across China using high-throughput sequencing. The alpha diversity of the rhizosphere was lower than that of bulk soil. The fungal community structures of the two soil compartments were distinct. Fungal communities in the rhizosphere had a steeper distance-decay relationship slope between sampled sites than those in bulk soil, suggesting a greater influence of historical processes (geographical separation) in the rhizosphere. The relative importance of dispersal limitation and environmental filtering for the fungal community composition differed between bulk soil and rhizosphere. Sloan neutral model analysis suggested that niche-based processes dominated the assemblage of fungal communities in the two soil compartments, while neutral processes had a weaker influence in the rhizosphere than in bulk soil. Additionally, we analyzed the structures of abundant and rare fungal sub-communities in each soil compartment. Rare sub-communities were more strongly influenced by dispersal limitation than abundant sub-communities. These results expand the current understanding of root-associated fungal community biogeography in agricultural soils on a large scale.