A Non-Compartment Approach to the Modeling of Carbon Cycle in Soils.
Yongsheng Feng, Univ of Alberta, Dept of Renewable Resources, Edmonton, AB T6G2E3, Canada and Xiaomei Li, Alberta Research Council, 250 Karl Clark Road, Edmonton, AB T6N 1E4, Canada.
Decomposition of SOC occurs over time scales that span 6 orders of magnitude, ranging from days for the decomposition of readily available soluble substrates to >1000 years for the humification and storage of the most stable forms of SOC. SOC is a complex mix of constituents with widely different chemical and physical characteristics. Most current models of SOC dynamics are “compartment models” that divide the total SOC into various conceptually homogeneous pools with different decomposition rates. Stabilization of SOC is described by flow of SOC among different pools during decomposition. There are several serious shortfalls of these models. Firstly, there is no firm connection among the conceptual homogeneous pools in the models and the measurable fractions of the SOC. Secondly, one can not identify a set of experiments that will, at least conceptually, uniquely determine all of the required parameters. Thirdly, the construction of the pools and the associated kinetic parameters are not unique: for any compartment model there can be infinitely other models with different kinetic parameters that produce identical predictions. The difficulties with compartment models can be avoided if one is willing to give up the first order decomposition equation and accept the fact that any identifiable fraction of SOC is kinetically complex. We have developed a continuous, non-compartment model of SOC dynamics based on the examination of fundamental processes of soil SOC cycle. The model and the parameters are based entirely on the observable characteristics of the SOC processes. A set of experiments is identified that, at least conceptually, uniquely determines all model parameters. The model can be applied either to the SOC as a whole, or to any identifiable fraction of the SOC. The performance of the model is illustrated by its ability to describe soil organic carbon processes over a broad span of time scales and by comparison with available experimental observations.