Bacterial inoculants improved the growth and nitrogen use efficiency of Pyrus betulifolia under nitrogen-limited conditions by affecting the native soil bacterial communities

Increases in crop yield are traditionally supported by the application of high doses of chemical fertilizers, which can have negative environmental impacts on ecosystems. Plant growth-promoting rhizobacteria (PGPR) are increasingly of interest due to their diverse agricultural benefits, but their effects on native soil bacterial communities and their related ecological roles are poorly understood. Currently, high-throughput sequencing provides an opportunity to gain insight into these aspects. The aim of this study was to assess the effects of three PGPR strains (Paenibacillus sp. RF2, Bacillus sp. RC25 and RC3) on the growth of Pyrus betulifolia seedlings under nitrogen (N)-limited conditions and to reveal whether they promote the succession of native soil bacterial communities involved in N supply. Our data showed that all strains significantly enhanced multiple growth parameters of P. betulifolia seedlings, and the strains were ranked in the order RC3 > RF2 > RC25 based on these effects. A similar pattern was also observed for soil urease activity and root vitality. As expected, bacterial inoculants changed the bacterial communities, and increases in the relative abundances of Ideonella, Pseudomonas, Pseudoduganella, Lactococcus and unclassified genera in Rhodocyclaceae and Comamonadaceae were observed with all or two of the inoculation treatments. The predicted results based on PICRUSt2 showed that all inoculation treatments significantly increased the relative abundances of nitrogenase. Furthermore, Ideonella and one unclassified genus in Rhodocyclaceae were mainly associated with nitrogenase and urease, and urease was also related to one unclassified genus in Comamonadaceae and Micropepsis. These results show that the tested strains could change native bacterial communities that take part in the N cycle and improve the N use efficiency of P. betulifolia seedlings under N-limited conditions. The information obtained in this study improves our understanding of the ecological roles of bacterial inoculants and identifies a potential strategy for enhancing the growth of P. betulifolia seedlings and reducing the use of chemical N fertilizer in breeding processes.