Field plants strategically regulate water uptake from different soil depths by spatiotemporally adjusting their radial root hydraulic conductivity

Plants modify their root hydraulics to maintain water status and strategically use soil water, but how they achieve this in the field conditions remains elusive. We developed a method to measure and calculate daily root water uptake, root water potential, and radial root water permeability at different depths in a wheat (Triticum aestivum L.) field and a permanent grassland dominated by ryegrass (Lolium perenne L.). During the drying processes, both plant systems reduced the radial water permeability of their shallow roots to limit topsoil water uptake, while increasing the radial water permeability of their roots in the subsoil to enhance water extraction. Conversely, after the topsoil was rewetted, both plant systems increased the radial water permeability of their shallow roots to enhance water extraction, while reducing the radial water permeability of their roots in the subsoil to limit water uptake. Root water uptake in the subsoil was more influenced by the topsoil water than by the subsoil water. The topsoil water serves both as a resource and a signal, coordinating optimal water uptake from different soil depths. These findings have important implications for understanding how plants cope with periodic water stress in the field and for screening drought-tolerant crop varieties.