Cellular automaton based modeling of dynamic soil structures and their functions across scales

We present a spatially and temporally explicit mechanistic model for soil aggregation at the microscale. This consists of a cellular automaton model for the dynamic rearrangement of solid building units whose size and shape are derived from dynamic image analysis of wet-sieved, water stable aggregates. This model is combined with a particulate organic matter (POM) turnover model or a model for a growing fine root which exudes and distributes mucilage into the soil. Along this line the mutually interacting soil and POM dynamics and the intertwined processes at the root-soil interface are captured and evaluated simultaneously at the biologically relevant scale. Our comprehensive modeling toolbox allows us to conduct various simulation scenarios and to discriminate and evaluate the underlying processes and different drivers such as texture. We quantify our results by evaluating the stability of the created structures or the dynamical change in local porosity around a growing root. Finally, the insights gained at the microscale are used to parametrize a CO2 transport model at the profile scale. Thereby, the microbially mediated CO2 source is taken into account as well as the driver soil texture, and changing ambient environmental conditions such as water saturation, oxygen concentration and POM content.