Grapevine responses to water deficit and N x K fertilization: Seasonal variation of ‘Cabernet Sauvignon’ and ‘Grenache’ physiology

Water and nutrient availability strongly influence grapevine yield and wine quality. While the single effects of water deficit and nutrient deficiency have been extensively studied, their interaction remains poorly understood. Two-year-old Vitis vinifera L. cv ‘Cabernet Sauvignon’ (near-anisohydric) and ‘Grenache’ (near-isohydric) plants grafted on SO4 were grown in pots under semi-environmental conditions. Plants were either maintained well-watered (100 % lysimeter evapotranspiration, ETlys) or subjected to water deficit (33 % ETlys) and treated with different nitrogen (N) and potassium (K) fertilization rates. Morpho-physiological analyses revealed that water deficit significantly reduced plant growth, with ‘Grenache’ exhibiting a slower growth rate than ‘Cabernet Sauvignon’. At flowering, water treatment was the dominant factor modulating plant response. Water deficit reduced stomatal conductance (gs), while enhancing accumulation of several nutrients. N and K fertilization became dominant factors during the following developmental stages: leaf ionomic composition of ‘Cabernet Sauvignon’ was responsive to N and K from veraison, and this behavior aligns with gs reduction caused by high N rather than water deficit. Conversely, the ionomic composition of ‘Grenache’ was affected by N and K only at maturity, while gs was consistently modulated by water availability throughout the season. K effects on leaf ionomic composition were more pronounced under high N. We highlighted the importance of both water and chemical inputs, whose effects vary with cultivar and developmental stage. Results will contribute to the improvement of viticultural sustainability by developing optimized fertilization strategies tailored to plant requirements under specific environmental conditions.