The importance of the hydraulic component connecting the roots to the soil

Comunicación presentada en el XIM4 4th Xylem International Meeting Padua, 25-27 September 2019Key message: The magnitude of the decline in water transport efficiency between root xylem to the root surface had clear consequences for stomatal closure and regulation of transpiration in olive plants early during water stress. Efficient water transport from soil to leaves sustains stomatal opening and steady-state photosynthesis. The above-ground portion of this pathway is well-described, yet the most important component lies below-ground and is poorly understood due to technical limitations. Here we used a novel rehydration technique to investigate changes in the hydraulic pathway between roots and soil and within the plant body as individual olive plants were subjected to a range of water stresses. Whole root hydraulic resistance (including the radial pathway from xylem to the root surface) constituted 82% of the whole-plant resistance in unstressed plants, increasing to >95% under a moderate level of water stress. The decline in root hydraulic conductance occurred in parallel with stomatal closure and contributed significantly to the reduction in canopy conductance according to a hydraulic model. Our results demonstrate that losses in root hydraulic conductance during moderate water stress in olive plants are profound and sufficient to induce stomatal closure before cavitation occurs. Future studies will determine whether this core regulatory role of root hydraulics exists more generally among diverse plant species.N