Résumé
Rhizodeposition - the diverse flows of organic matter released by living roots into the soil - varies significantly along root axes in interaction with spatial and temporal soil heterogeneity. It is thought that these flows are regulated by local root-soil carbon (C) and nitrogen (N) gradients, as well as the variations of light interception by leaves which influence C & N allocation between roots and shoot. However, the few available data on rhizodeposit flows along roots and their significance in plant balance are often fragmented by sampling techniques, scale, resource type, or growth stage. This compartmentalization hampers robust statistical analysis to evidence regulation patterns. To investigate the determinants of rhizodeposition and the contribution of exchange hotspots to plant C-N balance, we developed Wheat-BRIDGES, the first Functional-Structural Plant Model (FSPM) that links heterogeneous root and shoot resource acquisition with rhizodeposition through whole-plant ecophysiology. It integrates 3D shoot C-N-growth metabolism (CN-Wheat model), 3D root C-growth cycle (RhizoDep), water cycle (Hydroroot), N cycle and root anatomy (Root-CyNAPS). It simulates how soil conditions influences rhizodeposition, both locally through the short-term regulation of root-soil C-N-water exchanges, and at plant scale through the regulation of photosynthate production and allocation to roots. Using varying sowing densities to modulate the extent of competition for light and N, we identified active rhizodeposition regions that differed from those predicted by root models that rely on forced C inputs. Plant density, by modifying soil N distribution and C limitation due to shoot competition, led to contrasting effects on simulated root growth and rhizodeposition, which in turn altered the distribution of C-N fluxes from the roots within the soil profile. These results highlight Wheat-BRIDGES’ ability to decipher the complex spatial and temporal dynamics of root-soil exchanges, and how these interact with root & shoot metabolism and architecture within a heterogeneous environment.