October 2011 Meeting

Monday, October 10, 2011
6:00 - 7:30 pm

Pellissippi State Technical Community College
10915 Hardin Valley Road, Knoxville
J.L Goins Administration Building, Cafeteria Annex



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

Dr. Melanie Mayes
Oak Ridge National Laboratory
Oak Ridge, Tennessee


The top meter of soil contains 1500 Pg of carbon (C), twice that of the atmosphere and 3 times that of standing biomass. Contemporary models often simulate C dynamics by determining C pool characteristics, pool sizes and turnover rates on an ad hoc or post hoc basis. Consequently, soil C response to climate change is inadequately predicted in many circumstances. The goal of our project is to produce a mechanistic model of cycling of organic C (OC) in soils that can be linked into the global scale. We hypothesize that attachment at the interface with soil minerals will determine the bioavailability of OC to microbes, and thereby exert control over soil C turnover. The relationship between attachment and stabilization for common OC compounds (lignin, lipid, sugars, starch) is determined in batch sorption and long-term incubation experiments using a global suite of soils. The mineral fraction of surface soils appears to have greater apparent sorption than that of subsurface soils, which could indicate more effective degradation by microbes at the surface. We determine the mechanisms of sorption and its influence on OC stabilization using neutron reflectometry (NR) at the Spallation Neutron Source (SNS). We observe the formation of stacked layers of OC, and the arrangement is dependent upon the hydrophobicity of the OC compounds. The turnover of the OC compounds as they cycle through measurable soil pools (dissolved, mineral OC, particulate OC, 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. We have completed a literature review of over 100 publications to determine parameter values, and have coded and tested a simulation model for OC cycling in soils. The ultimate outcome is a validated, realistic, globally-relevant soil C model that is linkable into widely-used global circulation models.


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