Dose-dependent effects of Paenibacillus mucilaginosus on maize growth, rhizosphere soil properties, and bacterial community structure

Background and Aims Paenibacillus mucilaginosus is a plant growth-promoting rhizobacterium (PGPR), yet its optimal application dosage and the associated rhizosphere ecological responses remain poorly understood. This study aimed to evaluate the dose-dependent effects of P. mucilaginosus on maize growth, soil properties, and the rhizosphere bacterial community. Methods Maize was inoculated with three dosages of P. mucilaginosus (1×10⁵, 1×10⁶, and 1×10⁷ CFU/g). Plant growth parameters, leaf antioxidant enzyme activities, malondialdehyde (MDA) content, and soil nutrient contents were measured. Rhizosphere bacterial communities were characterized by 16S rRNA gene sequencing, and functional potentials were predicted using PICRUSt2. LEfSe and random forest analyses were employed to identify key taxa, and Spearman correlation analysis was performed to explore relationships between pathways and plant/soil parameters. Results Inoculation significantly enhanced plant growth, antioxidant enzyme activities, and soil nutrient contents in a dose-dependent manner, while reducing MDA content. The abundance of P. mucilaginosus increased significantly with increasing inoculation concentration. Inoculation reduced alpha diversity and altered beta diversity of the rhizosphere community. LEfSe and random forest consistently identified P. mucilaginosus as the core growth-promoting taxon. PICRUSt2 revealed enrichment of pathways related to amino acid metabolism, antibiotic biosynthesis, and protein export, which positively correlated with growth/antioxidant parameters and negatively with MDA content. Conclusion These findings indicate that P. mucilaginosus promotes maize growth and alleviates oxidative stress in a dose-dependent manner, effects likely linked to the restructuring of the rhizosphere bacterial community and the enrichment of specific metabolic functions, providing a scientific basis for its optimized application as a biofertilizer.