FIG. 10. Simulation of the propagation of a water uptake front across the root system of a 50-d-old narrowleaf lupin (Lupinus angustifolius) with a fibrous root system, growing in a sandy rhizotron. Length scale in centimeters. Distribution of calculated water uptake within the root system 1.5, 5, 7, 9, and 11.5 h after the beginning of an uptake experiment. The rates are expressed as flux density (i.e., volumetric flow rate normalized to the root surface area [cm³ cm^–2 s^–1]). The red lines show the downwardly moving zone of active water uptake. The green color shows negative flux rates, that is, water exsorption by roots (from Doussan et al., 2006).