Impact of severe water stress on drought resistance mechanisms and hydraulic vulnerability segmentation in grapevine: the role of rootstock

Severe water stress can lead to hydraulic disfunction, reducing plant conductance or even causing death. Some plants exhibit hydraulic vulnerability segmentation between organs to reduce this risk. However, its role in influencing drought tolerance and resistance in grafted plants, such as grapevine, remains unclear. This study evaluates the physiological responses, drought tolerance, hydraulic vulnerability segmentation, and xylem anatomy of 2-year-old Vitis vinifera cv. Tempranillo scion grafted onto two rootstocks: 110-Richter (110R) and Sélection Oppenheim 4 (SO4). After subjecting the plants to drought conditions until the onset of embolism in the leaf (water potential corresponding to 12% loss of xylem hydraulic conductivity, P12), we analysed the physiological consequences during recovery. Grapevine exhibits hydraulic vulnerability segmentation not only within scion organs but also between the scion and rootstock. Although no differences in scion drought tolerance and embolism resistance were observed between combinations, Tempranillo-110R exhibited higher leaf minimum conductance, leaf P12 values, and root biomass. In contrast, Tempranillo-SO4 displayed larger vessel diameter and higher hydraulic conductance. These differences may explain the slower recovery of Tempranillo-110R compared with Tempranillo-SO4, which showed higher stomatal and root-to-stem hydraulic conductance. These findings indicate that in selecting rootstock, consideration should be given to drought resilience alongside vigour and productivity, especially given the increasing occurrence of severe drought periods due to climate change.