Drivers of Biological Nitrogen Fixation in Paddy Soils: Linking Soil Properties, Diazotrophic Communities, and Nitrogen Dynamics

Biological Nitrogen Fixation (BNF) is a sustainable alternative to synthetic fertilizers that deliver bioavailable nitrogen to rice fields. However, the spatial variability of BNF and the relative contributions of soil physicochemical properties and trace-element availability remain poorly understood in long-term cultivated paddy soils. To address this knowledge gap, we conducted an incubation experiment using paddy soils collected from Zhejiang and Jiangxi provinces of China, and quantified BNF rates using acetylene reduction assay (ARA). BNF rates varied from 24 ± 3 to 368 ± 13 kg N ha−1 with substantial geographic variability (15.3-fold). We observed that soil BNF capacity of Zhejiang soils was much higher than in Jiangxi soils. Microbial community and correlation analysis revealed that Phylum Proteobacteria and genera Pseudomonas and Geobacter were abundant and showed positive association with high BNF sites. Redundancy analysis (RDA) and Random Forest modelling stated that available Molybdenum was the most important predictors of BNF. Overall, our findings demonstrated that soil physiochemical properties, micronutrient availability, and microbial community composition interact to regulate BNF in paddy soils.