The Role of Soil Minerals in Terrestrial Carbon Storage: Linking Field and Laboratory Studies with Complimentary Spectroscopy Methods

Abstract

Soils contain enough organic carbon to significantly influence climate change, but the geochemistry that controls the soil carbon cycle is poorly understood. Minerals in soils may interact with the organic carbon, preventing it from being decomposed and released as carbon dioxide, but the forms of these interactions are complex and debated in the literature. This study experimentally simulates the interactions by reacting pure forms of five key soil minerals with dissolved organic carbon, analyzing samples with X-ray absorption near-edge structure (XANES), Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), nuclear magnetic resonance spectroscopy ((^{1})H NMR), and infrared spectroscopy (IR). The experimental results are then compared with analyses of diverse soil samples. In both datasets, positively charged calcite and oxide surfaces stabilize oxygen-rich organic groups, while neutral clay surfaces interact with more neutral hydrocarbons, supporting the hypothesis that the mineral’s surface chemistry controls these interactions. A soil’s mineralogy may determine which forms of carbon are stored, informing soil carbon models that are currently oversimplified.