Challenges to Measuring and Modeling Soil Organic Matter Stability.

The ecosystem functions of soil organic matter (SOM) are a result of not only SOM quantity, but also SOM stability. SOM stability has important implications for the permanence and vulnerability of soil C stocks in response to disturbance and climate change. It generally refers to how easily C and nutrients in SOM can be mineralized by the microbial population and its enzymes, and is a function of a variety of stabilization and destabilization mechanisms.

SOM stability is implicitly embedded in current C turnover simulation models such as Century and RothC through the use of multiple compartments to reflect the heterogeneous nature of SOM with varying rates of decomposition. The problem, however, is that these are largely mathematical and statistical constructs, rather than mechanistic ones. The evolving challenge set by Schmidt et al. (2011, Nature) is the development of new quantitative and mechanistic methods for expressing SOM stability that can be incorporated into models.

This presentation will provide an overview of two novel approaches to quantitatively express SOM stability. The first is an energy-based approach where SOM stability is a function of high activation energy cost and low potential energy gain from decomposition. The second is a radiocarbon-based approach that thermally fractionates SOM rather than using a single, mean value. These approaches are presented as “straw men” meant to incite revulsion, debate, and ultimately improvements to our current conceptual and modeling paradigms.