Root water uptake modules used in large scale models often rely on simplistic assumptions. Besides simplifying the3-D root architecture into 1-D profiles, they also assume uniform and constant root properties, uniform horizontal soil properties at the plant scale, empirical relationships between actual transpiration and soil water status or constant root (xylem) water potential with depth. Most of these assumptions have been made for sake of simplicity, to avoid large calculation times, and because a lack of proper measurement techniques for roots. However, some of these simplifications are questioned today, especially when these simplified models are compared with real datasets.

Today, large computation power and improved non invasive techniques allow for a better characterization of the plant root properties and more complex models. A three-dimensional root water uptake model called R-SWMS has been built, in which 3D soil water flow and solute transport is coupled with the water flow equation in the plant xylem network. Such a model may be useful for estimating the sensitivity of plant or soil-related processes on the water flow in soil or on the plant transpiration. It may also be compared with root water uptake experiments to asses by inverse modeling root or soil hydraulic property dynamics. We will show applications of this model to assess the impact of soil and root properties on actual transpiration and show how solute uptake affects solute distribution under different uptake mechanisms.

Novel developments include the code parallelization of the root and soil water flow modules and the coupling with a particle tracker for solute transport. Another perspective is to use such models to better indentify relevant processes at the plant and the field scales in order to parameterize and develop simplified effective models.

It is a joint work with V. Couvreur, N. Schroeder, L. Beff and J. Vanderborght.