Functional bacteria isolated from the rhizosphere of mixed plantation promote the growth of Cunninghamia lanceolata by reshaping bacterial community structure

Mixed-species plantations can improve soil fertility and forest productivity by reshaping rhizosphere microbial communities, yet the functional roles of enriched bacteria remain poorly understood. We isolated three multifunctional rhizobacteria, X3 ( Sphingomonas sp.), X5 ( Roseomonas mucosa ), and GNC ( Pseudomonas sp.), from the rhizosphere of Phoebe bournei in a P. bournei–Cunninghamia lanceolata mixed plantation. Their effects on C. lanceolata were evaluated through plant growth, soil biochemical profiling, 16S rRNA sequencing, network analysis, and transcriptomics. Inoculation with all three strains enhanced plant growth, root development, photosynthetic performance, and phosphorus accumulation, accompanied by changes in soil pH, nutrient availability, phosphatase activity, and phosphorus fractions. Inoculation also reshaped rhizosphere bacterial community structure and enriched ASVs related to X3 and GNC in key network positions, although strain-level persistence could not be confirmed. Exploratory PLS-PM indicated associations linking microbial community attributes, soil properties, and plant growth. Transcriptomic responses involved pathways related to auxin signaling, root development, photosynthesis, and phosphorus acquisition. These findings support a model in which mixed-plantation-derived PGPR promote C. lanceolata growth through coordinated changes in rhizosphere microbial communities, soil phosphorus cycling, and host responses.