Science – King & Sokol (2025): Soil carbon formation is promoted by saturation deficit and existing mineral-associated carbon, not by microbial carbon-use efficiency
Alison E. King and Noah W. Sokol, IN: Science Advances, https://doi.org/10.1126/sciadv.adv9482
Mineral-associated organic carbon (MAOC) is the largest terrestrial pool of organic carbon, yet controls on its formation remain unresolved. Existing MAOC is thought to preclude additional C storage on minerals, but this perspective is difficult to reconcile with observations that MAOC stacks in multilayers, suggesting that existing MAOC could promote greater C retention. Here, in a manipulative experiment using 118 soils from 15 agricultural sites across the United States, the authors show that MAOC formation is promoted by both existing MAOC and its counterpart—MAOC saturation deficit.