Abstract
The adverse effects of heatwaves on viticulture could be, at least partly, mitigated by generous soil water availability. As climate change will also likely reduce irrigation water, knowing to which extent soil water availability could be decreased under the heatwaves without compromising plant performances would be important. In this pot experiment, we differentiated soil water availability by compensating 100% (T100), 70% (T70), 40% (T40) and 10% (T10) of vine transpiration. Grapevines (cv. Sauvignon) were then subjected to a 11-day heatwave (Tmax 40 °C) and to a post-heat stress recovery phase. Soil water potential between -0.05 to -0.2 MPa, respectively, in T100 and T70 enabled the plants to maintain high net CO2 assimilation (Pn), stomatal conductance (gs), and leaf transpiration (Eleaf) which kept the leaf temperature (Tleaf) below the ambient temperature and promoted the plant growth. During the heatwave, T100 and T70 vines decreased their photochemical yield and dissipated the excess energy via regulated non-photochemical heat dissipation, and resumed their photochemical activities upon removing the heat stress. Further reduction in soil water potential to -0.4 and and -1.2 MPa in T40 and T10, respectively, decreased Pn and gs and restrained Eleaf, causing a significant increase in Tleafduring the heatwave, and limited the plant recovery after the heat stress. Nonetheless, the maximum efficiency of PSII (Fv/Fm) showed quite high resistance to heat stress in all treatments. These findings suggest that decreasing soil water availability to reach soil water potential levels close to -0.2 MPa implies higher efficiency in using water resources during a heat wave without limiting plant growth.