Mucilage enables water uptake in cowpeas (Vigna unguiculata L.) under soil water deficit

Various rhizosphere traits have been explored as plant adaptations to modulate the soil-root interface to acquire resources and to enhance plant water status under stress conditions. Mucilage exudation has been suggested to enable water uptake during soil drying. This hypothesis was tested using artificial root analogy due to technical limitations and the lack of suitable plant materials. Here, we tested whether mucilage exudation facilitates water uptake in intact cowpeas (Vigna unguiculata L.) plants growing in loamy soil during drying. We used a root pressure chamber system to measure the gradients in water potential at the root surface as well as the relationship between transpiration rate and leaf xylem water potential in two genotypes with contrasting mucilage production. Higher mucilage exudation attenuated the drop in matric potential at the root surface. In contrast, the gradients in water potential were much steeper in cowpea with less mucilage production. The attenuation of matric potential at the root surface resulted in a linear relationship between transpiration rate and leaf xylem water potential. We conclude that mucilage exudation maintains the hydraulic continuity between roots and soil and decelerates water potential dissipation near the root surface during soil drying. Our findings provide the first in vivo evidence on the role of mucilage on root water uptake.