Drought responses in Chardonnay and Sauvignon blanc grapevine cultivars: Mechanistic insights and varietal contrasts

This study explored the responses of Chardonnay and Sauvignon blanc grapevine cultivars to water deficit across four years, uncovering their shared patterns and distinctive coping mechanisms. The research was conducted in a commercial vineyard located in Isla de Maipo, Chile. Various characterization approaches were employed including plant water potentials (Y), gas exchange measurements, shoot vulnerability curves, productivity assessments, and leaf cell water relations. Linear mixed models and sensitivity analyses were performed using various statistical methods to evaluate cultivar responses to water deficit. As the water deficit progressed, both cultivars displayed a parallel reduction in stomatal conductance, leaf turgor, and increased shoot embolism. Moreover, both cultivars exhibit a sigmoid decrease in yield as Y_leaf declined, highlighting a 50% productivity reduction corresponding to a 50% reduction in stomatal conductance. However, Chardonnay demonstrated higher drought tolerance, achieving more negative Y_leaf values during water deficit, with leaf turgor loss occurring at a lower Y threshold. Furthermore, differences in Y_leaf between the cultivars stemmed from their distinct drought-coping mechanisms. Chardonnay employed osmotic adjustment to facilitate water movement and maintain turgor, while Sauvignon blanc relied on elastic adjustment to sustain elevated leaf water content. Sensitivity analysis suggests the limited impact of osmotic adjustment on Chardonnay’s Y_leaf variability, emphasizing its function as a delayed response to water stress. Conversely, Sauvignon blanc’s higher bulk elastic modulus influences Y_leaf fluctuations more prominently, promoting rapid rehydration under water scarcity. These mechanisms determined Y_leaf magnitudes, with Sauvignon blanc exhibiting lower stress levels than Chardonnay.