Characterization of grapevine responses to water deficit and nutrient availability

Grapevine (Vitis vinifera L.) cultivation represents one of the most important agricultural activities in Europe. However, since 2018, the global vine and wine sector has faced significant challenges, with production volumes reaching historically low levels. These declines have been attributed to the increase of extreme climatic conditions and the spread of fungal diseases that have severely impacted many vineyards worldwide. Among the environmental factors that influence vine performance, the availability of water and mineral nutrients in soil plays a major role in determining crop yield and berry quality. Therefore, the development of strategies towards an improvement of both water and nutrient use efficiency is crucial for sustainable viticultural production. Moreover, beneficial microorganisms, such as arbuscular mycorrhizal (AM) fungi, can further promote plant fitness by improving nutrient uptake and increasing tolerance to abiotic stresses. While the single effects of water deficit and nutrient limitation have been extensively studied, their interactions remain poorly understood. The aim of this PhD research was to characterize the combined effects of water deficit and nutrient availability in grapevine cultivars with different sensitivities to water stress. The application of a multidisciplinary and multifactorial approach that integrates morpho-physiological evaluations with omic techniques and microbiological analyses provided an accurate description of grapevine varietal resilience to different edaphic conditions. In the first two experiments, young Cabernet Sauvignon (near-anisohydric) and Grenache (near-isohydric) plants grafted on SO4 rootstocks were grown in soil pots under semi-environmental conditions. In the first trial, plants were maintained either well-watered or subjected to a controlled water deficit and treated with different nitrogen (N) and potassium (K) fertilization levels. In the second trial, grapevine resilience to moderate and severe water deficit was assessed for two consecutive growing seasons, and the potential mitigating role of microbial application was also tested. Water deficit caused a significant reduction in plant growth and several physiological parameters, such as transpiration rate and stem water potential, while increasing the concentration of several macro- and micronutrients in leaves and roots. The moderate water deficit had only a mild effect on plant water status, while a more severe water deficit caused a stronger reduction in transpiration and stem water potential. Multielemental analysis at flowering stage revealed that leaf elemental composition was mainly affected by irrigation treatment. Conversely, the nutrient profile at the maturity stage was strongly influenced by N fertilization. A seasonal variation in plant response to water and N treatment was also observed at the physiological level, especially in Cabernet Sauvignon. In addition, the beneficial effects of microbial treatment were more pronounced under water deficit conditions, and in particular in Grenache. Nevertheless, water deficit was the most important factor that influenced rhizosphere microbial community composition. Finally, synchrotron-based elemental mapping revealed a distinct spatial distribution of elements across different leaf and root tissues depending on Fe availability and N forms. Overall, this research highlights the complex interactions among water availability, mineral nutrition, and beneficial microorganisms in grapevine. These findings stress the importance of considering irrigation and fertilization practices together for a more sustainable management of viticulture under a changing climate.