Biochar (BC) has garnered extensive attention as a carbon sequestration solution. This study comprehensively reviews of the effects of BC on the buildup, protection, stabilization, and mineralization of soil organic carbon (SOC). The input of BC-derived carbon alters soil carbon quality by changing SOC content and aromaticity. BC also affects processes controlling substrate accessibility, such as physical protection of SOC by soil aggregates and organo-mineral interaction. Changes in soil carbon quality and physicochemical properties further alter carbon source availability and microbial habitat, thereby affecting the microbial decomposition of SOC. Of particular importance is the soil aggregation process, which regulates the distribution and turnover of microbial necromass and SOC fraction in different aggregates. The microbial carbon pump concept framework highlights the pivotal role of microbial necromass in the formation of soil stable carbon pool. BC can affect the accumulation and decomposition of microbial necromass carbon in the bulk soil and different aggregates, thereby changing the soil carbon pool composition and stability. The newly proposed mineral carbon pump hypothesis further emphasizes the crucial role of organo-mineral interaction in stabilizing SOC. Further research is required to understand the role of viable microbial biomass and dead microbial necromass in SOC turnover, as well as the extent and mechanism of the interaction between BC and soil minerals. Long-term ecosystem effects of BC, as well as the resilience of BC-soil system to climate change, need to be clarified to determine the rationality of BC application in the context of global change.
