Rhizobia modulate the peanut rhizobacterial community and soil metabolites depending on nitrogen availability

The rhizobial inoculation effects on the peanut rhizosphere bacterial community and metabolites were studied under different N availability following the five N application rates without rhizobial inoculation (N1–N5; 0, 40, 80, 110, 170 kg N ha −1 ) or with rhizobial inoculation (RN1–RN5) in a 3-year field trial. The effects of rhizobia on peanut growth, the rhizobacterial community, and root metabolites differed depending on the N availability. Plant height and nodule number were significantly increased by rhizobial inoculation, especially in RN3. Rhizobacterial abundance and richness were increased by rhizobial inoculation, except in RN1 (no N added). The number of 16S rRNA gene copies was higher in RN1–RN3 than in N1–N3 in both years. The largest number of differential bacterial genera between an inoculated treatment and its corresponding uninoculated treatment was in RN1 vs. N1. The beneficial bacteria Saccharimonadales and c_JG30-KF-CM66 ( Chloroflexi ) were most abundant in RN3. The concentrations of organic acids (3-methylglutaric acid, adipic acid, 3-hydroxyoctanoic acid, and octenedioic acid) were significantly increased in RN3 and were positively correlated with c_JG30-KF-CM66 ( Chloroflexi ), soil available N, and biomass. No metabolic pathways were significantly enriched by rhizobial inoculation at the highest N application rate (RN5). These results demonstrate that rhizobia positively affect peanut growth and yield under the best N availability via their ability to reshape the soil microbiome and metabolites.