Under the global warming scenario, water scarcity is expected to intensify in most grape‑growing regions. The use of drought-tolerant rootstocks is considered a useful tool to mitigate the negative effects of soil water deficit on vine functioning. Differences in leaf gas exchange, plant water status, specific hydraulic conductivity in petioles (Kpetiole), xylem vessel size and vegetative vigour of field-grown Pinot noir grafted onto five rootstocks (3309C, 101-14 MGt, Kober 5BB, Riparia Gloire de Montpellier, 41B MGt) were investigated during one season under water deficit in Switzerland. The water deficit was imposed by installing waterproof and non-reflecting plastic sheets on the soil from March to harvest (September) to avoid rainfall infiltration. Rootstocks had stronger effects on vine water status than on gas exchanges. During the grape ripening stage, vines grafted onto 41B MGt and 101-14 MGt were characterised by more severe water stress as shown by the lowest values of pre-dawn leaf (Ψpd), stem water potential (Ψstem) and water stress integral (SΨ), whereas 3309C and Kober 5BB rootstocks induced milder effects. Significant differences in photosynthesis (A), stomatal conductance (gs) and transpiration (E) were only observed between vines grafted onto 41B MGt and 3309C at later stages of ripening. Changes induced by rootstocks in shoot vigour, Kpetiole and the number and size of xylem vessels in petioles and stems were correlated to differential responses of Pinot noir to water deficit. The increased vegetative vigour induced by 3309C and Kober 5BB was associated with the highest Kpetiole, xylem vessel size and a good plant water status of Pinot noir under low soil water availability. Kober 5BB induced the highest yield, probably due to the better vine water status, whereas vines grafted onto 41B MGt showed the lowest malic acid content and yeast assimilable nitrogen in berries.
