Organic Matter Stabilization: Mechanistic Insights at the Molecular and Nanometer Length Scales.

Humans have been releasing elevated levels of carbon dioxide into the atmosphere, causing the carbon cycle to run awry and accelerating the effects of climate change. Approximately 80% of Earth’s terrestrial carbon is stored in soil, and the residence time of this carbon can range from hours to hundreds or thousands of years. To date, detailed mechanisms describing carbon stabilization in soil is lacking, yet understanding the role of this carbon pool in the carbon cycle is crucial to both predicting climate and sustaining services such as provisioning of freshwater, food security, and human health.

It has been documented that soil organic carbon is strongly associated with both high surface area clay minerals and pre-existing organic molecules. The nature of these interactions is not well understood and much of the current knowledge relies on experiments that take a top-down approach using bulk experimental measurements. Our work seeks to systematically probe physical, chemical, and molecular-level interactions at organo-mineral and organic-organic interfaces using a bottom-up approach. By implementing dynamic force spectroscopy, we have explored the energy landscape of individual functional groups (including carboxylic acid, amine, methyl, and phosphate groups) to directly measure the binding energies of these organic moieties with clay and mineral surfaces. Using these measurements, we have generated a model system to determine chemistries that exhibit both strong and weak binding to minerals. This research has the potential to provide researchers with guiding principles about stabilization mechanisms of carbon in soils at the sub-nanometer length scale.