The global pool of organic matter (OM) in soils is roughly 1500 PgC, with a typical gross flux of approximately 60 PgC /yr. These numbers imply that the average turnover time of organic carbon in soils is on the order of 25 years. Carbon dating of OM, however, shows that certain forms of carbon become effectively removed from the global carbon cycle for thousands of years. Clearly, this is an important phenomenon to understand if we wish to have a coherent and holistic picture of the carbon cycle, and if we wish to understand the feedback loops between carbon sources and sinks, anthropogenic carbon production, and climate change. An emerging conceptual view is that this recalcitrance may be related to the multilayer sorption of organic molecules on mineral surfaces. Recent high-resolution mass spectrometry (FT-ICR-MS) analyses support this hypothesis and provide evidence of both a temporal selectivity and a subsequent structural layering of organic matter adsorbing to the basal surfaces of iron-bearing minerals (such as goethite, hematite and ferrihydrite) [1], which form some of the most prevalent mineral phases present in soils around the globe.<br/><br/>In the present study, we use molecular modeling to understand the processes driving the adsorption and subsequent recalcitrance of soil OM upon the iron-oxide mineral basal surface of goethite and the clay mineral smectite. Classical molecular dynamics simulations are used to understand the temporal fractionation of a representative set of soil organic matter (amino-acids, sugars, and lignin-like molecules) and its subsequent structural layering at the mineral-organic interface.

Molecular simulations of soil organic matter at the mineral-water interface

ACS Spring 2022

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