Biochar-based Bacillus subtilis inoculants promote plant growth: Regulating microbial community to improve soil properties

Numerous studies support the synergistic use of biochar (BC) and plant growth-promoting rhizobacteria to enhance plant growth. Despite this, the complex and dynamic nature of soil environments necessitates further exploration of the interactions between soil microorganisms and soil properties under BC-based inoculants. This study investigated their combined effects using a BC-based inoculant, Bacillus subtilis SL-44 (BC@SL), to explore the relationship between microorganisms and soil properties. Additionally, differentiating the effects of exogenous auxiliaries BC, SL-44, and BC@SL, which can promote plant growth, enhance plant and soil enzyme activities, regulate microbial communities, and increase soil nutrient content. Compared to BC alone, SL-44 enhances plant superoxide dismutase, peroxidase, and catalase enzyme activities, while BC increases soil cellulase and urease activities. SL-44 elevates Bacillus content, whereas BC boosts overall microbial abundance. Although initial values of most soil properties remain stable under exogenous auxiliaries, by the fourth week, soil pH and organic matter decrease, while electrical conductivity, available phosphorus, and ammonium nitrogen increase significantly across treatments. BC@SL, integrating the advantages of both BC and SL-44, exhibits superior performance. Under BC@SL treatment, Bacillus content rises from 4.36% to 14.96%, and available phosphorus and ammonium nitrogen increase by 81.97% and 53.16%, respectively. Additionally, plant dry weight increases by 51.95%. These results highlight the effectiveness of BC@SL in microbial regulation, soil nutrient enhancement, and plant growth promotion. In summary, BC@SL proves to be a stable and efficient solid soil additive, supporting the advancement of green fertilizer practices.