Fundamental Considerations of Soil Organic Carbon Dynamics: A New Theoretical Framework

The dynamics of soil organic carbon (SOC) decomposition have received renewed attention in recent decades because of the concerns over its potential feedback to predicted climate change. At present, the dominant theory of SOC decomposition is based on the idea that SOC consists of kinetically homogeneous compartments decomposing according to first-order kinetics. A simpler and more consistent theoretical framework is developed based on the view that SOC is a population of carbon with widely distributed ages, along with three fundamental assumptions-that of the possibility of steady state, linearity, and rate-time equivalence. The new theory bases its description and prediction of SOC dynamics on a single observable SOC decomposition function, the R function. A number of different measurements of SOC decomposition are shown to be connected by R. Accurate description and prediction of SOC dynamics over a wide range of time scales are obtained based on approximation of R by a simple two-parameter "hockey stick" function. Previously perceived inconsistencies in experimental observations, particularly in the determination of SOC turnover time and the response of SOC decomposition to temperature, are shown to be consistent with the new theory. The new theoretical framework can serve as the foundation for more consistent interpretation of experimental observations and for the development of more robust process-based predictive models of SOC.