Conifer and broadleaf trees show a strong co-evolution with rhizosphere diazotrophic microbiome

Background and Aims Free living, non-symbiotic nitrogen-fixing bacteria (diazotrophs) that inhabit plant rhizosphere substantially contribute to nitrogen input in forest ecosystems. Different plant species provide heterogeneous habitats for rhizosphere diazotrophs by releasing root exudates containing potential resources for microbial utilization, but the ecological processes of diazotrophic community assembly and association with plant species are not fully understood. Methods We investigated the diazotrophic abundance (as assessed by real-time quantitative PCR), diversity, and composition of rhizosphere diazotrophic communities (based on nifH -amplicon sequencing) for four non-leguminous broadleaf tree species and three conifer tree species in a forest ecosystem. Results The analysis revealed that the rhizosphere of four broadleaf tree species harbored higher diazotrophic abundance and diversity by 239% and 50.0% respectively, as compared to the conifer tree species. Further, phylogenetic distance between the seven tree species was positively correlated (Mantel r = 0.482, P