Differences in water-use-efficiency between two Vitis vinifera cultivars (Grenache and Tempranillo) explained by the combined response of stomata to hydraulic and chemical signals during water stress

• Grenache is more recommendable for drought prone areas.
• Tempranillo and Grenache showed differential regulation of leaf water relations.
• Abscisic acid can exert a differentiating role on stomatal control.

Knowledge about regulation of stomatal conductance is necessary to improve grapevine water use efficiency. The vast range of grapevine cultivars may allow choosing the best-performing ones to global changing conditions provided the understanding and characterization of their physiological responses. In this study, a comparison between two cultivars (Tempranillo and Grenache) with different reputation in water use efficiency was performed during two experimental years in field-conditions. Water relations, leaf gas exchange and abscisic acid (ABA) dynamics were measured at different phenological stages along the growing seasons. A clear difference in the regulation of leaf water relations was observed between cultivars under water stress conditions. Specifically, results showed that there is a clear relationship between hydraulic conductance (Kh) and stomatal regulation. However, ABA can exert a differentiating role on stomatal control during different stages within the grapevine growth period. Furthermore, this study showed that differences in osmotic adjustment could lead to substantial differentiation in the stomatal regulation and the leaf water use efficiency.