A new, offer versus demand, modelling approach to assess the impact of micro-organisms spatio-temporal population dynamics on soil organic matter decomposition rates

We used the multi-agent MIOR simulator as an exploratory tool to discuss some basic modelling principles as regards soil organic matter (SOM) decomposition processes, which are viewed as the result of interactions between the soil living community (represented by MM micro-organisms entities) and the “dead” organic matter (the SOM resource represented by individualized OM entities). In this paper we formalize the original offer-demand mechanism implemented in MIOR in a way that allows for the comparison of different conceptual points of view as regards the best way to couple biologically based population models (for the decomposer dynamics) and physically based first-order kinetic models (for the decomposed substrate). We show that accounting for explicit interactions leads to the introduction of effective decomposition rates which vary in time as a function of the M/C living (M) versus dead (C) matter carbon content ratio. More generally, by means of numerical experiments, we show that, as soon as we account for temporal or spatial variations of the microbial biomass, it brings into question the classical way to estimate a constant SOM decomposition rate from soil carbon content decay data.