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 remains elusive. We developed a method to measure and calculate daily water uptake, water potential and radial hydraulic permeability of roots at different depths in wheat and permanent grass fields. During drying processes, both plant systems decreased the radial hydraulic permeability of their shallow roots to reduce water uptake from the topsoil, while increasing the radial hydraulic permeability of their deep roots to boost water uptake from the subsoil. Conversely, after the topsoil was rewetted, both plant systems instantly increased the radial hydraulic permeability of their shallow roots to enhance water uptake from the topsoil whereas decreasing the radial hydraulic permeability of their deep roots to reduce water extraction from the subsoil. We found water uptake of deep roots was influenced by topsoil water more than by subsoil water, and thus the topsoil water serves not only as a resource but also as a cue coordinating optimal use of soil water in different depths. These findings have important implications for improving our understanding of the mechanisms plants use to cope with periodic water stress and screening drought-tolerant varieties.