Radial branch hydraulics and cellular injury thresholds in poplar: insights from controlled dehydration and high-resolution dendrometry.

Branch water release and radial exchange influence drought responses. Although mechanistic models describe radial hydraulic and storage dynamics, experimental quantification of hydraulic capacitance (C) and radial resistance (Rr) across broad ranges of xylem water-potential (Ψx), particularly under severe dehydration, remains limited. We quantified how C and Rr vary with Ψx in Populus albaL., assessed the value of coupling controlled osmotic dehydration with high-resolution dendrometry, and evaluated cellular damage and bud viability across increasing dehydration levels. Branch segments were subjected to stepwise, experimentally induced dehydration by perfusion with D-sorbitol solutions (-1 to -4 MPa) to impose stable and controlled Ψx. Branch diameter dynamics and equilibration plateaus were used to estimate C and Rr, and diameter-derived pressure-volume curves were fitted using the Sureau model. Electrolyte leakage and bud development were monitored to assess injury and recovery capacity at the organ level. D-sorbitol equilibrated rapidly along the xylem with limited bark infiltration, and stepwise decreases in Ψx induced characteristic diameter contractions enabling robust extraction of C and Rr. Both traits varied with Ψx: C peaked at intermediate Ψx (-1 to -2 MPa) and declined under severe dehydration, while Rr increased steadily as Ψx decreased. Electrolyte leakage increased and buds failed to resume growth below -2 MPa. Controlled osmotic dehydration combined with high-resolution dendrometry enables precise quantification of C(Ψx) and Rr(Ψx) and reveals physiologically meaningful thresholds associated with cellular injury and loss of recovery capacity at the organ level, providing a useful framework for dehydration-tolerance phenotyping.