The dominant genera of nitrogenase (nifH) affects soil biological nitrogen fixation along an elevational gradient in the Hengduan mountains.

Biological nitrogen (N) fixation by diazotrophic microbes is an essential process for the N input. However, the patterns of biological N fixation and its biological or environmental mechanism along an elevational gradient in mountain ecosystems are not fully understood. In this study, a field experiment was conducted in the Hengduan Mountains to investigate the biological N fixation associated with the diversity and abundance of the nifH gene. Our results showed that both the abundance of the nifH gene and the biological N fixation displayed hump-shaped trends along an elevation gradient in the wet and dry seasons. However, the diversity of the nifH gene showed an inverse unimodal trend along an elevation gradient. We observed that biological N fixation was jointly associated with the abundance of the nifH gene, especially dominant genera, as well as soil chartacteristics. Among them, clay content played a preeminent role in the regulation of N fixation potentially through the formation of microaggregates and microenvironments. In general, our results revealed that biological N fixation was correlated with the abundance of microorganisms, especially dominant genera, and soil texture. These results highlighted the importance of dominant genera, which should be considered in the modeling and forecasting of N cycling under future environmental change.