Biochar modulates soil microbial communities via reactive oxygen species derived from its constituents

Biochar can effectively suppress soil-borne pathogens and improve soil bacterial community structure. However, its underlying antibacterial mechanisms remain unclear, limiting its targeted application. This study systematically evaluated the direct antibacterial effect of biochars derived from four straw types at varying pyrolysis temperatures (300–700 °C) against Ralstonia solanacearum through in vitro assays, material characterization, and pot experiments. Tobacco stem (TS) biochar exhibited strong antibacterial activity. Analysis of influencing factors combined with quenching experiments identified reactive oxygen species (ROS) as the principal antibacterial mechanism, with a clear temperature-dependent production pathway. Biochar produced at 300–400 °C primarily generated free radicals (•OH and •O2−), achieving 92.91% to 99.60% inhibition, while those pyrolyzed at 500–700 °C predominantly contained non-radical ROS (1O2 and H2O2) and reached 100% inhibition. Rhizosphere bacterial community analysis indicated that TS biochar increased bacterial richness (Chao1 index raised by 497.77–951.34), microbial network complexity and stability (nodes increased by 82–136; edges by 1224–2185). Artificial soil experiment confirmed that TS biochar elevates soil ROS levels and directly modulates the microbial community. These findings elucidate the temperature-driven ROS-mediated regulatory mechanism of biochar and provide key insights for targeted biochar amendments against soil-borne pathogens.