Effect of Bacillus velezensis on the structure of the rhizosphere microbial community and yield of soybean

The beneficial effects of Bacillus on crop growth have been confirmed in various contexts. However, the impact of exogenous Bacillus application on the rhizosphere microbial community throughout the entire growth cycle of soybean remains unclear. This study investigated the soybean cultivar 'Qihuang 34' under three gradient treatments: Control, no Bacillus application, 0 kg/ha(CK), low Bacillus application, 15 kg/ha(BL), and high Bacillus application, 30 kg/ha(BH), analyzing the dynamic changes in rhizosphere soil microbial community structure and their effects on yield across different growth stages (vegetative(V2), flowering(R2), fruiting(R4) and pod-filling(R6)). The results showed that bacterial α-diversity indices were generally higher at the vegetative stage than at flowering, pod-setting, and seed-filling stages, with inconsistent variation patterns across growth periods. The relative abundance of dominant bacterial phyla and genera varied over time. In the BL treatment, the relative abundances of Rhizobiaceae, Sphingomonadaceae, and Pseudomonadaceae significantly increased at the R4 and R6 stages (p < 0.05). In the BH treatment, the relative abundance of Fusarium decreased by 16.16% (R4) and 65.21% (R6) compared to CK. Correlation analysis between soil physicochemical properties and microbial phylum-level composition revealed that total nitrogen (TN) and total sulfur (TS) were the primary drivers of rhizosphere bacterial communities, while TS played a key role in shaping fungal communities. Additionally, the BH treatment significantly increased soybean yield by 4.50-13.84% (p < 0.05). This study provides foundational insights into how Bacillus influences the composition and diversity of soybean rhizosphere microbial communities, supporting the development of sustainable agricultural practices through rhizosphere microbiome management.