Control factors of soil diazotrophic community assembly and nitrogen fixation rate across eastern China

Biological nitrogen (N) fixation is an essential N input into terrestrial ecosystems and plays a critical role in global N cycling. However, the driving factors of the diazotrophic community composition and soil N fixation rate at the regional scale remain largely unclear, especially in different land-use types. Here, we explored the environmental adaptation of diazotrophic communities and controlling factors of N fixation in maize, rice, and forest soils across eastern China. Results showed that the diversity, composition, and co-occurrence network differed significantly among these habitats, with a relatively higher alpha diversity and network complexity in rice fields. The mean annual precipitation plays a predominant role in shaping diazotrophic community composition. Dispersal limitation, belonging to stochastic processes, contributed most to diazotrophic community assembly in terrestrial ecosystems. Habitat niche breadth analysis indicated that the environmental adaptation of diazotrophic communities was highest in rice fields, followed by forest and maize fields. The overall N fixation rate was higher in rice fields, followed by maize and forest soils. Structural equation modeling revealed that the N fixation rate was mainly affected by soil properties in maize and forest soils. In contrast, the N fixation rate was more influenced by diazotrophic community composition and climatic factors in rice habitats. Our results revealed that the environmental adaptation of the diazotrophic communities and controlling factors of the N fixation function were different among maize, rice, and forest ecosystems. These findings will help us understand and predict the N bioavailability in different ecosystem types under climate changes.