Carbon sequestration in soil affected by mineral-doped biochar: Roles of soil aggregate and microbial community

Biochar's inherent stability and porous structure contribute to soil organic carbon (SOC) preservation by reducing mineralization and enhancing carbon input, but there are still knowledge gaps of the mechanism. This study prepared biochar doped with fly ash and coal gangue (FA/BC and CG/BC) and investigated the effects of FA/BC and CG/BC on soil carbon components through soil incubation. The results indicated that mineral doping significantly increased the biochar yield (6 % more than initial biochar), facilitated porous structure formation, promoted the transformation of amorphous carbon into graphitic structure, thereby improving the antioxidant capacity (approximate 17.5 % less carbon loss) and thermal stability (1.5 %–6.8 % more carbon retention). FA/BC and CG/BC improved soil hydrolase activity, enhanced the structure and stability of soil aggregates, as well as reduced the bioavailability of dissolved organic matter. CG/BC with the content of 2.3 % exhibited the best effect on soil organic carbon, which increased microbial biomass carbon, particulate organic carbon and mineral-associated organic carbon by 138.2, 3.5 and 0.5 mg/kg, respectively, and decreased dissolved organic carbon by 48.9 mg/kg. According to Metagenomics results, biochar had a positive effect on soil microbial diversity, increasing the abundance of carbon-degrading genes and SOC-degrading enzymes that contributed to the accumulation of microbial biomass carbon. Overall, these above findings demonstrate that CG/BC enhances the structure and stability of soil aggregates, increases soil organic carbon (SOC) content, and elevates the abundance of functional microorganisms, thereby promoting the formation of stable SOC. The results emphasizes that mineral-doped biochar exhibits excellent carbon sequestration potential.