Grapevine adopts different strategies in response to drying regimes. Procrastinator or escaper?

Grapevines (Vitis vinifera) experience diverse drought conditions that can differ in severity, duration, and progression. In this study, we investigated the physiological, biochemical, and hormonal responses of the Barbera grapevine, a near-anisohydric cultivar, to two contrasting drought imposition regimes: a gradual stress mimicking field conditions (progressive drought, PD) and an abrupt stress simulating pot experiments (rapid drought, RD). We analyzed stomatal conductance (gs), stem water potential (Ψ), xylem sap pH, abscisic acid (ABA) levels, and non-structural carbohydrate (NSC) accumulation in xylem sap and leaves during stress and recovery. RD induced a rapid drop in Ψ and gs, accompanied by significant xylem sap alkalinization and a sharp rise in ABA concentration, which promoted early stomatal closure and rapid starch remobilization. In contrast, PD resulted in delayed stomatal closure, minimal ABA accumulation under moderate stress, and progressive xylem sap acidification, which facilitated osmotic adjustments via sustained accumulation of soluble sugars and ions. Our findings suggest that Barbera vines shift between isohydric and anisohydric behaviors depends on drought imposition dynamics. This physiological plasticity reflects a context-dependent deployment of stress avoidance or tolerance mechanisms. These insights emphasize the importance of stress imposition protocols in drought physiology studies and inform irrigation management and breeding programs for drought-resilient cultivars.