Hydraulic and physiological determinants of drought resilience in Chardonnay and Sauvignon blanc under Mediterranean conditions

Abstract

Sustainability in Mediterranean viticulture increasingly depends on optimizing water use without compromising vine function, yield, or terroir expression. Grapevine cultivars differ widely in their hydraulic traits and water-use strategies, yet the physiological determinants of these differences remain insufficiently understood. This study examined how two early-ripening white cultivars, Chardonnay and Sauvignon blanc, respond to field-imposed water stress during berry ripening in a commercial vineyard representative of central Chile’s Mediterranean terroirs. Physiological measurements were used to characterize stomatal regulation, leaf hydraulic traits, and xylem vulnerability to embolism under two irrigation regimes. Chardonnay exhibited lower stomatal sensitivity to declining water potential, maintaining higher stomatal conductance and leaf hydraulic conductance (k_leaf) under moderate stress compared with Sauvignon blanc. This behavior was associated with a greater leaf hydraulic capacitance (0.060 ± 0.002 MPa⁻¹ vs. 0.053 ± 0.003 MPa⁻¹) and higher thresholds for 50 % k_leaf loss (−1.00 ± 0.10 MPa vs. −0.85 ± 0.10 MPa) and turgor loss (−1.94 ± 0.14 MPa vs. −1.76 ± 0.14 MPa). Despite these quantitative differences, both cultivars showed coordinated declines in gas exchange and leaf water status, suggesting a shared drought-response pattern. No evidence of acclimation mechanisms, such as osmotic adjustment or xylem anatomical modification, was detected over the experimental period. Interestingly, the contrasting stomatal sensitivities did not translate into significant differences in integral water-use efficiency or yield, implying physiological compensation between hydraulic and photosynthetic processes. These findings indicate that deficit irrigation during berry ripening may exert only moderate impacts on Chardonnay and Sauvignon blanc productivity and water-use efficiency in Mediterranean climates. Understanding such cultivar-specific hydraulic thresholds offers practical value for site- and terroir-adapted irrigation management, supporting water conservation without compromising grape quality.