Tolerance to 1 year of drought: The role of seed hydration memory in the germination and early seedling development of <scp> <i>Xiquexique gounellei</i> </scp> subsp. <scp> <i>gounellei</i> </scp> under prolonged water deficit

Abstract Seed hydration memory can provide ecophysiological advantages, enhancing seedling competitiveness and influencing species establishment in environments with limited water availability. This study aimed to evaluate the effects of hydration–dehydration cycles (HD cycles) on seed germination and initial development of Xiquexique gounellei subsp. gounellei seedlings subjected to prolonged water deficit. Seeds were subjected to 0, 1, 2, and 3 HD cycles, each consisting of 5 h of hydration followed by 3 h of dehydration. The Germination Memory Index (GMI) was then calculated using daily germination data. After a 2‐month acclimatization period, seedlings underwent irrigation cycles of 7, 14, and 28 days, and morphological parameters were assessed at the end of the 28‐day period. Then, irrigation in all treatments was suspended for 360 days, after the third morphological assessment conducted during the seedling growth period. After this period, the morphological and biochemical evaluation of the reducing sugars was carried out. The seedlings were irrigated and then the parameters were evaluated again. The GMI confirmed, for the first time, the presence of hydration memory in this species, even under optimal water conditions, suggesting an inherent adaptive capacity. Treatment with two HD cycles was most effective, enhancing early growth in terms of height, stem diameter, root length, and biomass. HD cycles trigger physiological mechanisms linked to hydration memory, improving drought resilience. Notably, all seedlings survived the year‐long drought. These findings demonstrate that hydration memory remains functionally active beyond germination, throughout seedling development, and even after extended periods of water deficit.