Incorporating Molecular-Scale Mechanisms Stabilizing Soil Organic Carbon into Terrestrial Carbon Cycle Models

The top meter of soil contains 1500 Pg of carbon, twice that of the atmosphere and 3 times that of standing biomass. Contemporary soil carbon cycling models simulate the dynamics of soil carbon pools, but determine pools, pool sizes, and turnover rates post-hoc. Consequently, models have difficulty with prediction of carbon fluxes due to environmental change and over expanded or compressed spatio-temporal scales. A mechanistic representation of the cycling of organic carbon in soils has been produced that will link into regional and/or global models. We hypothesize that the strength and extent of chemical attachment at the interface with soil minerals will determine the bioavailability of carbon to microbes, and thereby exert control over soil organic carbon turnover times. The relationship between attachment and stabilization for common organic carbon compounds (lignin, lipid, sugars, starch) are determined in batch sorption and long-term incubation experiments using a global suite of soils. The mechanisms of attachment are determined using a coupled application of neutron reflectometry and molecular dynamics simulation. The turnover of the organic carbon compounds as they cycle through measurable pools (dissolved, mineral organic carbon, particulate organic carbon, and microbial biomass) are modeled through the mechanism of enzyme-facilitated microbial degradation. The model framework is developed and validated using published data, followed by application using our coupled sorption and degradation measurements on global soils. The ultimate outcome is a validated, realistic, globally-relevant soil carbon model that is linkable into widely-used global circulation models.

Program Development Accomplishments

The work begun here on model development and the companion sorption/incubation experiments will be continued and advanced in the 2013-2015 Terrestrial Ecosystem Science Focus Area (TES-SFA) sponsored by the Biological and Environmental Research (BER) Division.