Rhizosphere biophysics and root water uptake

The combination of soil drying and a high transpiration rate causes severe water stress in plants. In their Viewpoint article, Carminati et al. develop a biophysical model to describe how low soil moisture and high transpiration rates result in dramatic reduction of xylem water potential occurring across the rhizosphere as the soil dries, eventually leading to root dehydration and loss of contact with the soil.

Conceptual model of root water uptake including the effect of mucilage and root hairs. (A) Illustration of the spatial distribution of mucilage in the rhizosphere and the related increase in water content. The hypothesis is that mucilage increases the soil water content around the roots and keeps the space between root hairs wet and possibly conductive. (B) Putative profiles of water content as a function of distance from the root surface, including the effect of mucilage and root hairs. (C) Putative profile of matric potential as a function of distance from the root surface, including the effect of mucilage and root hairs. Three key questions to be addressed with high priority are highlighted.

Plants adopt several mechanisms that could attenuate such drops in water potential and facilitate root water uptake. In particular, mucilage exudation and root hairs can act as a bridge between the root surface and the adjacent bulk soil, thereby maintaining the hydraulic connection across the rhizosphere.

This paper is part of the Root Biology Special Issue.