Two Clones, Two Paths: divergent intrinsic xylem traits and hydraulic responses to prolonged drought in poplar.

BACKGROUND AND AIMS: Climate change is increasing the frequency and intensity of droughts, challenging the growth, hydraulic function and survival of woody plants. Poplar is a fast-growing species widely cultivated for biomass and cellulose production, but it is also highly sensitive to water deficit, with substantial variation among species and clones. METHODS: This study compared the drought responses of two Populus×canadensis clones, 'Tucano' and 'San Martino', under gradually imposed, prolonged water stress. Physiological traits and intrinsic wood anatomical characteristics revealed different strategies between clones for coping with drought. KEY RESULTS: 'Tucano' clone exhibited faster stomatal closure under moderate stress compared to the 'San Martino' clone and a greater resistance to embolism formation. The resistance was further supported by specific intrinsic wood anatomical traits, including higher vessel density, increased vessel clustering, greater theoretical hydraulic conductivity, thicker cell walls and higher wood density. Conversely, the delayed stomatal closure, the less negative P50 value, and the distinct xylem anatomical structure observed in 'San Martino' suggest a significantly higher vulnerability to prolonged water deficit. CONCLUSIONS: 'Tucano' adopts an effective drought-avoidance strategy, integrating stomatal regulation, intrinsic wood anatomy and carbon allocation to balance hydraulic safety with growth and wood quality. The study highlights specific traits as key determinants of drought resistance and supports the selection of specific clone for poplar cultivation in future climate scenarios characterized by water scarcity.