Impact of cultivar on grapevine physiological adaptation to drought and subsequent rehydration

Introduction Understanding grapevine responses to water deficit and rewatering is essential for developing adaptive strategies to mitigate the negative impacts of climate change in Mediterranean viticulture. Methods This study evaluated the ecophysiological and biochemical behaviour of two emblematic Douro cultivars, Touriga Franca (TF) and Tinto Cão (TC), subjected to contrasting water regimes under potted controlled conditions. Physiological measurements of gas exchange, chlorophyll a fluorescence, relative water content (RWC), and leaf biochemical parameters (photosynthetic pigments, phenolic compounds, flavonoids, soluble proteins, soluble sugars, and antioxidant activity) were performed after drought and recovery phases. Results revealed distinct adaptive responses between cultivars. Results and discussion TF exhibited moderate stomatal regulation, maintaining photosynthetic activity and high intrinsic water use efficiency during drought, as well as rapid recovery after rehydration. Conversely, TC showed a more conservative strategy, characterized by earlier stomatal closure, higher water retention (RWC > 90%), and increased accumulation of soluble proteins and phenolic compounds under stress. Both cultivars activated photoprotective mechanisms, with TF showing enhanced non-photochemical quenching and TC maintaining stable photosystem II efficiency. These findings highlight the contrasting strategies of TF (more anisohydric, plastic, and rapidly recoverable) and TC (more isohydric, conservative, and resilient), offering valuable insights for the selection of drought-tolerant cultivars and sustainable management of Douro vineyards under future warming and aridity scenarios.