Modelling the Functional Role of Microorganisms in the Daily Exchanges of Carbon between Atmosphere, Plants and Soil

There has been considerable research on organic carbon (OC) stocks in the upper layer of the soil but it has focused on semi-mechanistic predictions of OC stocks in the long term rather than on microbial processes acting on OC transformations. Published data lack of reference concerning the modelling of the short-term exchanges between atmosphere, plants, rhizobia and other microorganisms of soil. We think it is because the mechanistic role of microorganisms is poorly considered in most of the existing models. Compartmental theory is the most used to model the complex system of OC forms, with linear or no-linear propositions. Sometimes, the models did not consider explicitly an active microbial compartment and were often over parameterized. In contrast, the MOMOS proposition defined linearly the functional role of microorganisms with only a no-linear term linked to microbial respiration. It uses only 7 kinetic parameters having a clear ecological definition and being related to climate (all parameters), soil texture or pH (microbial respiration), and biological properties of debris inputs (enzymatic breakdown of plant debris and microbial mortality). The 3 other parameters (rates of humus stabilisation and enzyme assimilation of labile and stable humus) were found linked only to climate, suggesting that quality of humified materials should be more constant than OC forms from living materials. In coupling with soil water and production modules, the model emerges as a new theoretical basis to describe the life cycle and its applications to agro-ecology and global change.