Adapting viticulture to climate change: A four-year field trial on the role of water restriction in mitigating temperature increases in Malbec and Bonarda

Understanding the impact of rising environmental temperatures on Vitis vinifera is crucial for the wine industry in the context of global warming. This study investigated the combined effects of elevated daytime temperatures (ET) and moderate irrigation restriction (IR) at post-veraison, over four seasons in two widely cultivated cultivars in Argentina: Malbec and Bonarda. An open-top chamber with a passive air heating system was used to increase average daytime temperatures by approximately 2 °C. In general, vegetative growth parameters were not affected by ET or IR throughout the study, indicating no cumulative effects. Bonarda yield was reduced by ET due to fewer berries per bunch, and lighter berries and clusters, but remained unaffected by IR. In contrast, Malbec maintained stable yields under both ET and IR, suggesting greater adaptability. In both cultivars, ET led to increased sugar accumulation and higher alcohol content in wines, but also reduced wine colour intensity, colour index, and co-pigmented anthocyanins, while there were cultivar-specific differences. Despite these common negative effects, Malbec showed favourable traits under ET, including improved anthocyanin stability (higher proportions of acylated forms) and increased hue. The IR treatment restored colour intensity and increased the total polyphenol index in both cultivars, and also recovered colour index in Malbec. Overall, our findings suggest that Malbec exhibits greater phenotypic plasticity and potential for high-quality wine production under moderate post-veraison water stress and elevated temperature, compared to Bonarda. This irrigation strategy may help mitigate some of the adverse effects of elevated temperature by preserving wine colour and stability without significantly compromising vine growth or yield.