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Feng 2012

Dissertation/Thesis

Testing the Soil Carbon Saturation Theory: Maximal Carbon Stabilization at Soil Organic Matter Stability as a Function of Organic Carbon Inputs

Feng, Wenting (2012)
A Dissertation in Earth and Environmental Science, Presented to the Faculties of the University of Pennsylvania in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy  

Abstract

Soil carbon (C) stocks and fluxes represent significant components of the global C cycle. Application of the soil C saturation theory can help identify soils with large C storage potentials and estimate rates and durations needed to reach maximal soil C storage.

The goal of my dissertation was to test the soil C saturation theory by estimating C saturation levels of fine soil particles and quantifying changes in soil organic matter (SOM) stability as fine soil particles approach C saturation. Current model using least-squares linear regression generally underestimates C the maximal amount of soil C stabilization in fine soil particles.

Using an analysis of published data, I proposed two alternative methods (boundary line analysis and the organic C loading method) to improve estimates, and found that while the organic C loading method is better since it incorporated mineral specific surface areas which would influence C saturation, it requires information about soil mineralogy and further tests to determine whether the monolayer-equivalent C loading indeed represents a maximal C stabilization potential. Laboratory batch sorption experiment of dissolved organic matter onto soil minerals generated organo-mineral complexes with a range of organic C loadings. These organo-mineral complexes, as well as silt+clay fractions physically isolated from soil samples from three long-term agroecosystem field experiments with differing fertilizer and manure addition treatments, were used to test for differences in SOM stability as a function of organic C loading.

Biological, chemical, and thermal test of SOM stability showed little change or the increase trend of SOM stability with increasing organic C inputs, which do not support the notion of the soil C saturation theory that SOM stability decreases as organic C inputs increase. This observation of SOM stability is likely due to the fact that most samples did not exhibit C saturation behavior. The results show that most soils are likely well below C saturation, and further studies of the driving factors (e.g., chemical composition of organic C inputs, mineralogy, and organo-mineral binding types and strength) is needed to determine maximal C loadings and estimate the maximal soil C storage potentials.

Citation

Feng, Wenting (2012): Testing the Soil Carbon Saturation Theory: Maximal Carbon Stabilization at Soil Organic Matter Stability as a Function of Organic Carbon Inputs. A Dissertation in Earth and Environmental Science, Presented to the Faculties of the University of Pennsylvania in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy.