Incorporating Physicochemical Protection by the Soil Matrix Into Biogeochemical Models.

Current widely used models of SOC decomposition dynamics are based on the use of conceptual SOC pools described by first-order kinetics. A considerable amount of experience has been gained in using these models especially in regard to rate coefficient relationships with soil temperature and moisture conditions, soil texture, as well as interactions with N dynamics and microbial N transformations. However, the influence of the soil matrix through determining soil structural stability and soil C saturation has never explicitly been considered in these models. Recently, our understanding of how the interactions among particulate organic carbon, mineral associated organic carbon, and soil mineral particles interact to form aggregates and determine soil C saturation leves has increased. Here, we present several attempts to incorporate this new knowledge into SOC models. These SOC model introduce several features not encompassed by current soil decomposition models: 1) Alignment of model dynamics with measurable C pools and 2) Soil C Saturation behavior limiting SOC stabilization. All current decomposition models rely on first-order kinetics and, therefore, total SOC at equilibrium increases linearly with increased C inputs. However, if SOC transformations depend on mineral particle surface area and access to these surfaces, which is a function of aggregate dynamics, then there may be limits to the rate at which SOC can be transformed to stable forms. We will present proof-of-concept models that were validated by available observations for the parameters and coefficients used.