Soil pH correlates with the co-occurrence and assemblage process of diazotrophic communities in rhizosphere and bulk soils of wheat fields

Biological nitrogen fixation contributes to the pool of plant-available N in both bulk soil and the rhizosphere. Here we investigated the co-association and assemblage process of diazotrophic community members in both rhizosphere and bulk soil of wheat fields. The diazotrophic community structure in the rhizosphere was significantly different and comprised a less competitive and more stable network structure when compared with that of the bulk soil. Deterministic versus stochastic community assemblage processes were quantified using betaNTl scores, demonstrating that deterministic processes decreased in importance with distance from plant roots. Soil pH was correlated with diazotrophic community structure and diversity, and community structure showed greater connectivity and stability in soils with neutral pH relative to those in acidic or alkaline soils. Stochastic processes dominated the assemblage of the diazotrophic community in soils with neutral pH, while deterministic processes dominated in acidic or alkaline soils. These results suggest that soil pH may play an essential role in the interaction and assemblage processes of the diazotrophic community in the rhizosphere and bulk soils, which could enhance our understanding of biological nitrogen fixation in agricultural soils.