Modelling the continuous exchange of carbon between living organisms, the soil and the atmosphere

Abstract

AimsThis study evaluated a framework for modelling the continuous exchange of carbon (C) between the atmosphere, plants, humus, and microorganisms, proposing a plant C model coupled to MOMOS, an existing microbial C model.MethodsC data were collected on low fertility cereal-legume cropping systems. Plant C and microbial C were modelled simultaneously and the growth parameters of plants and nitrogen-fixing microorganisms were fitted to the data.ResultsAll C exchanges were successfully predicted using the same weather correction for plant and microbial processes. Most of the photosynthetic production was allocated to the roots, reducing yields. The C losses were found modelled mainly by root respiration for cereals, probably as an energy source for nutrient explorings, and by root mortality for legumes as a growth source for decomposers and symbiotic nodules. The effect of root-nodule activity on shoot growth was found non-linear. The system was modelled as a sink of 4.2 Mg C ha-1 year−1 in the soil’s labile C reserve.ConclusionsThis paper coordinates theoretical bases for modelling the processes regulating plant productivity associated with plant C losses. The tool appears to be robust and is now available for calculating the essential parameters of agro-ecology and climate change

Modelling the continuous exchange of nitrogen between microbial decomposers, the organs and symbionts of plants, soil reserves and the atmosphere

“…Jensen et al (2010) reported substantial savings of N fertilizer by symbiotic fixation of faba bean cropping systems and the need to increase associated knowledges about the N exchanges between roots and microorganisms. Ibrahim et al (2016) have used the Momos model, coupled with a soil water model and a plant production module, to simulate the continuous exchanges of C in intercropping of durum wheat and faba bean. This has allowed for example to estimate separately root tissue respirations and microbial respiration as attempted by Morell et al (2012) with the Motor model (Verberne et al, 1990).…”

“…This has allowed for example to estimate separately root tissue respirations and microbial respiration as attempted by Morell et al (2012) with the Motor model (Verberne et al, 1990). This paper aims to extend the study of Ibrahim et al (2016) to the continuous N exchanges between the same living organisms, the soil and the atmosphere. The objective was to test the equation system as a new tool to simulate the N exchange flows using measurements of state variables available in the field experiment of Ibrahim et al (2016).…”

“…This paper aims to extend the study of Ibrahim et al (2016) to the continuous N exchanges between the same living organisms, the soil and the atmosphere. The objective was to test the equation system as a new tool to simulate the N exchange flows using measurements of state variables available in the field experiment of Ibrahim et al (2016). For a model not over parameterized, the values of the flow parameters must converge to a unique set of solutions independently of the set of initial values.…”

“…For a model not over parameterized, the values of the flow parameters must converge to a unique set of solutions independently of the set of initial values. The inputs of N to microorganisms can be calculated from MOMOS-C simulation of the death of each organ and symbiont of each plant (Ibrahim et al, 2016) divided by its corresponding C-to-N ratio (which can be available in data bases). The modelling method should enable to estimate threshold values of microbial C-to-N ratio regulating immobilization or mineralization of inorganic N from decomposer microorganisms.…”

“…And simultaneously to estimate essential parameters of N exchanges for plant growth: time functions of absorption of inorganic N by roots, N fixation by symbiosis, N transfers to roots, shoots, grains, and N losses in environment. Such estimations complementary to that of Ibrahim et al (2016) must help to clarify essential points of ecosystem functioning such as: (i) how do decomposer organisms affect N accessibility or depletion for plant roots, is microbial homeostasis a valid assumption to control N exchanges in the legume-cereal system? (ii) how do the N exchanges between living organisms affect flows of photosynthesised C and crop yields?…”