Grapevines are frequently exposed to climatic extremes such as drought and high temperatures. Theoretically, hydraulic failure in grapevines can arise through two pathways: reduced soil moisture or high atmospheric demand (VPD). Although embolism formation under soil drought is well established, whether extreme atmospheric demand alone can trigger cavitation in well-watered grapevines remains uncertain.
To address this question, we exposed young grapevines (Vitis vinifera cv. Chardonnay) plants to acute heating, gradually increasing chamber temperature to 50 °C while maintaining irrigation. Despite exposure to extreme VPD (> 8 kPa), no embolism was detected in leaves. Instead, plants exhibited rapid stomatal closure, a collapse in photosynthetic efficiency (Fv/Fm), and severe reductions in gas exchange at 50 °C. Importantly, both PSII efficiency and photosynthetic parameters fully recovered once plants were returned to 25 °C, and recovery was sustained the following day, confirming the absence of hydraulic failure.
These results demonstrate that grapevine leaves can tolerate acute heat and high VPD without xylem embolism when water supply is not limiting, revealing a greater degree of hydraulic resilience than previously assumed. The findings highlight that functional decline under heat stress arises from reversible physiological impairment rather than irreversible cavitation, with significant implications for predicting vineyard responses to future climate extremes.
