Linking thermal and conventional measures of soil organic matter stability

The identification, isolation and characterization of labile and resistant fractions of soil organic matter (SOM) have received a great deal of scientific interest because of their implications in the permanence of SOM during sequestration and vulnerability of SOM in response to disturbance or climate change. A large number of biological, physical, and chemical fractionation procedures have been developed to distinguish between SOM that is more (labile) or less (resistant) easily decomposed by the soil microbial populations and its enzymes, but to date no single fractionation technique has been developed that adequately describes the complete continuum of SOM that exists in nature. Thermal analysis techniques have shown promise in measuring changes in the complete SOM stability continuum in whole-soil samples and isolated fractions. We compare conventional biological and chemical means to characterize SOM stability with results of thermal analyses. Acid hydrolysis, hot water extractable carbon and CO2 respiration are used as conventional means to assess SOM stability, while thermogravimetry (TG) and differential scanning calorimetry (DSC) are used as thermal means. The underlying assumption of many interpretations of SOM thermal analyses is that thermal stability is directly linked to biogeochemical stability. The current study seeks to test the validity of this assumption.