Anisohydric behaviour in grapevines results in better performance under moderate water stress and recovery than isohydric behaviour

Three grapevine varieties original from different climates: Grenache, from Mediterranean origin; Syrah, from mesic origin and Chardonnay, from the humid zone of Burgundy (France) were used to study differential physiological responses to water deficit and sub-sequent recovery after re-watering. Moreover, the effect of the environmental growing conditions on water use efficiency (WUE) was also studied. Changes of the lamina hydraulic conductance (K (lamina) ), transpiration, photosynthetic CO2 assimilation (A (N) ), stomatal conductance (g (s) ), mesophyll conductance to CO2 (g (m) ), chlorophyll fluorescence, and their interactions with other environmental conditions were followed during prolonged water stress and subsequent re-watering in Chardonnay, Grenache and Syrah. Grenache confirmed its reputation as isohydric and Chardonnay as anisohydric, but Syrah, a variety often considered as anisohydric, showed near-isohydric behaviour. Chardonnay displayed higher hydraulic conductance during both irrigation and water stress and a faster recovery after water stress as compared to the two isohydric-behaving varieties. Chardonnay attained lower decreases in stomatal conductance in response to water stress by delaying its adjustment of the lamina hydraulic conductance (K (lamina) ), which in turn resulted in the maintenance of higher photosynthesis and photosynthetic capacity, favoring faster recovery upon re-watering. The results do not support the common assumption that isohydric behaviour results in a better performance under water stress conditions. Indeed, under moderate water stress, Chardonnay showed some advantages over the two varieties displaying near-isohydric behaviour. Integrated over a period including water stress imposition, acclimation and recovery Chardonnay displayed higher CO2 assimilation than Grenache and Syrah, which implies a higher yield potential under these conditions.