Mechanisms of soil carbon preservation illuminated by model mineral-associated organic matter

A central control on atmospheric CO 2 is the stabilization of organic carbon in soils. While there are well-described properties associated with stable soil carbon, such as interactions with minerals and conserved chemical features, determining the mechanisms underlying these properties is challenged by soil complexity and heterogeneity. Here we synthesize a naturally complex, tunable model form of mineral-associated organic matter (LabMAOM) to explore mechanisms of stable soil carbon formation and persistence. We show that mineral association and ambient organic matter synergistically stabilize LabMAOM against microbial decomposition. Moreover, different starting compositions of organic matter yield a conserved final LabMAOM chemical composition consistent with natural soils. Our findings open new mechanistic understanding of stable soil carbon and will be of utility to climate modeling and soil health management.