Mutual interactions of organic matter with soil minerals: kinetics, adsorption modes, transformation and stability of complexes

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Soil organic matter (SOM) is the most important sink for organic carbon in terrestrial ecosystems. Adsorption of SOM by mineral surfaces is one of the major stabilization mechanisms that decelerate the decomposition of SOM. SOM comprises a variety of organic compounds with different chemical structures and properties, potentially interacting with minerals. However, the mechanisms of the mutual interactions of these chemical compounds with soil minerals, and the impacts of these interactions on the stability of both SOM and minerals in SOM-mineral complexes are not yet clarified. In the proposed project, we suggest a novel approach considering composition and structure of both SOM and minerals. We plan to carry out a systematic study on the mutual interactions of important SOM constituents (phenolic acids, cutin monomers, peptides) with soil minerals – montmorillonite, and Fe and Mn oxides (ferrihydrite, birnessite) of varying crystallinity. We will study the fast kinetics to estimate the mode and energy of SOM adsorption by minerals. We will apply state-of-the-art analytical techniques (LC/MS and XPS) to elucidate the mechanisms of competitive or cooperative adsorption and transformation of different SOM compounds by minerals, and the impact of these interactions on the stability/alteration of the oxides. We will apply two scenarios to investigate adsorption and transformation of organic compounds by minerals, and to shed light on the formation of SOM-mineral complexes under natural conditions: simultaneous addition of the compounds to minerals, or addition of a competitor to a mineral with pre-adsorbed compounds. We will also investigate the impact of changing redox conditions on the stability of SOM and SOM-mineral complexes. Our novel experimental results and conceptual conclusions will advance the understanding of the mechanisms of SOM-mineral complex formation, and elucidate the environmental fate of SOM and minerals.