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2599094 
Journal Article 
Soil carbon saturation: Implications for measurable carbon pool dynamics in long-term incubations 
Stewart, CE; Paustian, K; Conant, RT; Plante, AF; Six, J 
2009 
1 
Soil Biology and Biochemistry
ISSN: 0038-0717
EISSN: 1879-3428 
41 
2 
357-366 
WOS:000263398400023 
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 (13)C- 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 (13)C 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. (C) 2008 Elsevier Ltd. All rights reserved. 
Agroecasystem; Carbon sequestration; (13)C labeling; Particulate organic matter; Soil aggregation; Soil incubation; Soil carbon saturation; Soil organic matter stabilization