Deciphering the distinct mechanisms shaping the broomcorn millet rhizosphere bacterial and fungal communities in a typical agricultural ecosystem of Northern China

Microbes play an essential role in agricultural ecosystems; however, the processes that drive the microbial biogeographic and co-occurrence patterns have rarely been assessed simultaneously, especially in the broomcorn millet rhizosphere. In this work, we explored the spatial distribution and association networks of bacteria and fungi in the rhizosphere of broomcorn millet selected from 12 locations across northern China using high-throughput sequencing. We decomposed the β-diversity into species turnover and nestedness, confirming that the bacterial and fungal β-diversity in the broomcorn millet rhizosphere was almost entirely linked to species turnover. Distance-decay relationships revealed that the biogeographic patterns of rhizosphere bacterial and fungal β-diversity (including species turnover rather than nestedness) were clearly distinct. Environmental selection was the only factor determining the rhizosphere bacterial β-diversity, whereas the rhizosphere fungal β-diversity was governed by both environmental selection and dispersal limitation. We also demonstrated that mean annual temperature (MAT) and pH were the major ecological drivers regulating the bacterial and fungal community structure, keystone species, and modularisation in the broomcorn millet rhizosphere. This elucidated different mechanisms of bacterial and fungal biogeographic and co-occurrence patterns in the broomcorn millet rhizosphere, and provided new ideas and basic insights for an in-depth understanding of the biogeography and coexistence theory of broomcorn millet rhizosphere ecosystems.