Bradyrhizobial peanut inoculant competitiveness is associated with rhizosphere microbiota

Inoculating legumes with selected rhizobial inoculant strain(s) to promote legume growth affects rhizosphere microbiota, yet the effects of inoculation vary. We isolated rhizobia from peanut root nodules collected across Sichuan, China, assessed their symbiotic performance in greenhouses and at two field sites with different soil types and climates, determined their competitiveness against native strains using rpoB amplicon sequencing, and assessed inoculation-related differences in peanut rhizosphere bacterial and fungal communities using 16S rRNA gene and ITS amplicon sequencing. Four of the eight strains utilized as inoculants in the field experiments were competitive against native soil rhizobia. The differences in structure and taxonomic composition of rhizosphere bacterial and fungal communities were mostly noted between the sites. The number of differentially abundant rhizosphere genera was greater at the site with no prior peanut cultivation history than at the site in the traditional peanut cultivation areas. In the latter, differentially abundant genera were detected only in treatments where the inoculants were enriched in peanut nodules. The results provided minor support for the hypothesis that competitive inoculants would affect rhizosphere communities more than uncompetitive and ineffective inoculants, and that the effects of inoculation would be larger at a site with no peanut cultivation history. However, differences in the rhizosphere microbiota were likely to depend more on the local microbiota or soil conditions than on inoculation.