Calcium is associated with specific soil organic carbon decomposition products

Abstract. Calcium (Ca) may contribute to the preservation of soil organic carbon (SOC) in more ecosystems than previously thought. Here we provide evidence that Ca is co-located with SOC compounds that are enriched in aromatic and phenolic groups, across different acidic soil-types and locations with different ecosystem properties. In turn, this co-localised fraction of Ca-SOC is removed through cation-exchange, and the association is then only re-established during decomposition in the presence of Ca (Ca addition incubation). Thereby highlighting a causative link between decomposition and the co-location of Ca with a characteristic fraction of SOC. Incorporating this mechanism into conceptual and numerical models can improve our understanding, predictions, and management of carbon dynamics in natural and managed soils, and account for their response to Ca-rich amendments.