A comparison between water uptake and root length density in winter wheat: effects of root density and rhizosphere properties

Background and aims: We aim to quantify the variation in root distribution in a set of 35 experimental wheat lines. We also compared the effect of variation in hydraulic properties of the rhizosphere on water uptake by roots.
Methods : We measured the root length density and soil drying in 35 wheat lines in a field experiment. A 3D numerical model was used to predict soil drying profiles with the different root length distributions and compared with measured soil drying. The model was used to test different scenarios of the hydraulic properties of the rhizosphere.
Results : We showed that wheat lines with no detectable differences in root length density can induce soil drying profiles with statistically significant differences. Our data confirmed that a root length density of at least 1 cm/cm3 is needed to drain all the available water in soil. In surface layers where the root length density was far greater than 1 cm/cm3 water uptake was independent of rooting density due to competition for water. However, in deeper layers where root length density was less than 1 cm/cm3, water uptake by roots was proportional to root density.
Conclusion : In a set of wheat lines with no detectable differences in the root length density we found significant differences in water uptake. This may be because small differences in root density at depth can result in larger differences in water uptake or that the hydraulic properties of the rhizosphere can greatly affect water uptake.