Strain-Specific Fungal-Bacterial Co-Inoculation Regulates Rhizosphere Microecology and Plant-Soil-Microbiome...

Beneficial fungal-bacterial interactions are important drivers of rhizosphere microecology and plant-soil functional coupling in conifer seedling systems, but their strain-combination-specific effects remain insufficiently understood. In this study, Pinus sylvestris var. mongolica seedlings were inoculated with three plant growth-promoting rhizobacteria (PGPR) strains, Serratia plymuthica A13, Acinetobacter lwoffii A07, and Pseudomonas koreensis A20, the ectomycorrhizal fungal strain Suillus luteus N94, and their corresponding co-inoculation combinations. Seedling growth, root architecture, plant nutrients, soil nutrients, soil enzyme activities, bacterial and fungal communities, differential taxa, network key taxa, and plant-soil functional indices were analyzed. Different inoculation treatments produced treatment- and trait-specific responses, with several N94-PGPR combinations showing advantages in particular growth, root, and soil functional traits, while some single-inoculation treatments also showed distinct positive effects. N94_A20 showed the greatest increases in seedling height, total dry weight, soil available phosphorus, and soil multifunctionality, whereas N94_A07 showed the strongest root architecture response and relative interaction index. Co-inoculation also reshaped rhizosphere bacterial and fungal communities and generated treatment-specific microbial enrichment patterns. Massilia, Ramlibacter, Holtermanniella, and Naganishia were positively associated with plant-soil functional indices. These results indicate that PGPR-N94 co-inoculation promotes conifer seedling growth through coordinated changes in root architecture, nutrient acquisition, soil biochemical function, and rhizosphere microbial community assembly.