Abstract:The elevational distribution of soil microbial diversity has been extensively studied, however, the distribution pattern of soil diazotrophic community along elevational gradient in root zone of a single woody plant is still unclear. Based on the Illumina high-throughput sequencing, soil diazotrophic diversity, community composition and spatial distribution in root zone of 161 Ginkgo biloba trees with elevation from 308 m to 1 236 m in the Tianmu Mountain, Zhejiang Province were investigated. The results show that diazotrophic diversity (Shannon and Richness indexes) significantly decreases along elevation. Diazotrophic community dissimilarity increases with the increase in elevation distance, and relative abundances of dominant genera such as Bradyrhizobium, Rhizobium and Verrucomicrobium are significantly and positively correlated with elevation, while relative abundances of the genera such as Geobacter, Azotobacter and Burkholderia are significantly and negatively correlated with elevation. Besides, both diazotrophic diversity and community composition are mostly correlated with soil N:P ratio. In addition, relative abundances of dominant diazotrophic genera are significantly correlated with soil N:P rat io. Structural equation modelling analyses show that elevation can directly or indirectly affect diazotrophic diversity and community composition by affecting soil N:P ratio. Random forest model analysis identifies species clusters are closely related to elevation and N:P ratio, respectively, and these two clusters have a large proportion (45%) of overlap. In summary, soil N:P ratio is the key factor in determining elevational distribution of soil diazotrophs in root zone of G. biloba in the Tianmu Mountain, and the change in soil N:P ratio can directly affect diazotrophic community of G. biloba. Our findings provide scientific basis in the conservation of wild G. biloba in the Tianmu Mountain from the view point of soil microbiology.