Distribution characteristics of endophytic bacteria and endophytic nitrogen-fixing bacteria in Vicia faba root nodules in rocky desertification areas of Southwest China

Understanding bacterial communities in leguminous root nodules is crucial, as they are key pioneer plants for restoring degraded soil ecosystems. This study collected root nodule samples from wild Vicia faba across four rocky desertification sites in Honghe, Yunnan, China. The diversity of endophytic bacteria, including nitrogen-fixing bacteria, in these nodules were analyzed using 16S rDNA and nifH sequencing. A total of 451 bacterial Operational Taxonomic Units (OTUs) were identified, with Proteobacteria as the dominant phylum and Pseudomonas and Rhizobium as the predominant genera. Notably, bacterial community composition varied significantly among the four areas. Rhizobium positively correlated with available phosphorus content and rocky desertification degree but negatively correlated with soil water content (SWC). These findings indicate that available phosphorus, rocky desertification degree, and SWC are key factors influencing the endophytic bacterial community in Vicia faba root nodules. A total of 309 OTUs representing nitrogen-fixing bacteria were identified; again, Proteobacteria was dominant, with Bradyrhizobium and Rhizobium being most prevalent. Significant variations in nitrogen-fixing bacterial communities occurred across sampling sites. Key physicochemical factors affecting this community' s structure included total phosphorus, total nitrogen, and pH. These results may provide a theoretical basis for developing biological control strategies to mitigate rocky desertification.