Soil carbon saturation: Implications for measurable carbon pool dynamics in long-term incubations |
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Authors: | Catherine E Stewart Keith Paustian Richard T Conant Johan Six |
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Institution: | a Department of Geological Sciences, University of Colorado, Boulder, CO 80309-0399, USA b Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523-1499, USA c Department of Soil and Crop Sciences, Colorado State University, Fort Collins, CO 80523, USA d Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA 19104-6316, USA e Department of Plant Sciences, University of California, Davis, CA 95616, USA |
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Abstract: | The efficiency of agricultural management practices to store SOC depends on C input level and how far a soil is from its saturation level (i.e. saturation deficit). The C saturation hypothesis suggests an ultimate soil C stabilization capacity defined by four SOM pools capable of C saturation: (1) non-protected, (2) physically protected, (3) chemically protected and (4) biochemically protected. We tested if C saturation deficit and the amount of added C influenced SOC storage in measurable soil fractions corresponding to the conceptual chemical, physical, biochemical, and non-protected C pools. We added two levels of 13C-labeled residue to soil samples from seven agricultural sites that were either closer to (i.e., A-horizon) or further from (i.e., C-horizon) their C saturation level and incubated them for 2.5 years. Residue-derived C stabilization was, in most sites, directly related to C saturation deficit but mechanisms of C stabilization differed between the chemically and biochemically protected pools. The physically protected C pool showed a varied effect of C saturation deficit on 13C stabilization, due to opposite behavior of the POM and mineral fractions. We found distinct behavior between unaggregated and aggregated mineral-associated fractions emphasizing the mechanistic difference between the chemically and physically protected C-pools. To accurately predict SOC dynamics and stabilization, C saturation of soil C pools, particularly the chemically and biochemically protected pools, should be considered. |
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Keywords: | Agroecosystem Carbon sequestration 13C labeling Particulate organic matter Soil aggregation Soil incubation Soil carbon saturation Soil organic matter stabilization |
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