Résumé
Root systems combine traits with a large range of functional plasticity, e.g. in response to heterogeneous soil conditions. This plasticity is thought to be driven in particular by a tight coupling between carbon (C), nitrogen (N) and water (W) fluxes, both between roots and soil at a millimetric scale and within the whole plant itself. The few available data illustrating spatial and temporal variations in C-N exchanges along the roots suggests complex regulatory patterns, which appear difficult to interpret with our current interpretation tools. Functional-Structural Plant Models (FSPM) provide a frame for integrating incomplete data in a mechanistic way , but existing root models consider either C, N, W, or growth physiology separately, without retroactive effects on each other. We propose a novel architectured FSPM, Root-RIDGES, that describes C, N, and W transport and transformation at the root segment scale, and then integrate these processes along a growing root system. The model has been built combining existing or recently-developed 3D root models with novel processes, e.g. N-W uptake, C-N biosyntheses and maintenance, C-N rhizodeposition, and growth regulation by C-N availability. We used Root-RIDGES to simulate plant-soil C-N exchanges and root growth during the vegetative stage of winter wheat. Boundary conditions were simulated by a 1-dimensional soil model accounting for organic matter mineralization and by the CN-Wheat shoot model. Our simulations showed contrasted responses of the roots depending on the local availability of soil mineral N, with important consequences on the spatiotemporal distribution of rhizodeposits within the soil profile and their share in the overall C-N budget of the plant. This model therefore represents a unique tool to realistically scale and study the individual contributions of different plant organs to the soil-plant-atmosphere system dynamics.