Stomatal closure prevents the drop in soil water potential around roots.

Keywords: hydraulic conductivity; rhizosphere; root-soil contact; soil drying; stomata; transpiration EN hydraulic conductivity rhizosphere root-soil contact soil drying stomata transpiration 1541 1543 3 05/20/20 20200615 NES 200615 The recent paper by Rodriguez-Dominguez & Brodribb ([9]) shows that the loss in soil-root hydraulic conductance is the primary constraint on water flow during water stress (soil water potential below -1 MPa) and that this initiates stomata closure. This is an important result as it highlights the link between stomatal regulation and belowground soil-root interactions, particularly those taking place at the root-soil interface and in the adjacent soil, the I rhizosphere i . Remarkably, as the soil dried out, root and soil-root interface hydraulic conductances dropped significantly and became the primary constraint on water flow, more than xylem cavitation. Despite stomatal closure alleviating the loss of soil hydraulic conductance I K i SB soil sb , soil drying caused a large drop of hydraulic conductance at the root-soil interface I K SB i sb i . [Extracted from the article]