For the first time ever, a functional–structural root-system model (FSRSM) is validated by combining a tracer experiment monitored with magnetic resonance imaging and three-dimensional modeling of water and solute transport. This study is the first that combines 4D (space and time) root system architecture with spatially resolved measurements of root-zone tracer concentrations to validate/parameterize a FSRSM. We have shown that R-SWMS, a FSRSM, can properly represent water and solute fluxes in the root zone. Moreover, 3D tracer distribution maps were demonstrated to contain valuable information for inferring the hydraulic parameters of roots of different orders and ages. The parameter set obtained was in the range of other previous studies of lupin plants. This great work by Axelle Koch (UCLouvain) and colleagues is published in Journal of Experimental Botany. You can download it here .