Bridging the Microbial and Mineral Carbon Pumps: Biochar for Synergistic Soil Carbon Sequestration

Enhancing soil carbon sequestration is a pivotal strategy for mitigating global climate change. Integrating the "microbial carbon pump (MCP)" and "mineral carbon pump (MnCP)" frameworks is essential for a holistic understanding of soil organic carbon (SOC) stabilization. While biochar (BC) is a recognized carbon sequestration tool, the mechanistic pathways by which it mediates the synergy between these distinct carbon pumps remain elusive. This review synthesizes current advances to position BC as a critical "bridge" driving the coupled MCP-MnCP system. Beyond serving as recalcitrant carbon, BC strengthens the MCP by providing microbial habitats, optimizing community structure, and enhancing carbon use efficiency to promote necromass accumulation. Simultaneously, BC fortifies the MnCP via mechanisms including the formation of stable organo-mineral complexes through surface functional groups, the facilitation of microaggregate genesis, and the mediation of redox reactions. This bridging efficacy offers a novel theoretical framework for developing predictable, controllable soil carbon technologies. Furthermore, we explore the theoretical basis for integrating BC into the coupled MCP-MnCP system. Future research must prioritize cross-scale mechanistic dissection, advance the precision design of BC functionality, and incorporate its "dual carbon pump" enhancement effects into life cycle assessment frameworks to fully realize its potential in climate mitigation and sustainable agriculture.