Fig. 1. Schematic of the reactive transport model at the pore-scale.
O2(g) diffuses from the atmosphere (gas phase) and is dissolved to the liquid phase (O2(aq)) according to Henry’s law. Simultaneously, dissolved organic carbon (DOC) is released from soil organic matter (OM). In the presence of both O2(aq) and DOC, aerobic heterotrophic respiration occurs at the interface between the aqueous phase (blue) and the surface of soil grains (brown) by attached microbes (biofilms). As a result, CO2(aq) is released to the water and to the atmosphere CO2(g). In the inset, a scanning electron microscope image shows a cluster of bacteria (bluish colored) around a micrometer root (brown); false coloring was applied for illustration purposes.