Plant water stress detection and the effect on grapevines hydraulic functioning

Under predicted climate change scenarios, water management is becoming worldwide an increasingly important issue which is reflected in the introduction of concepts like water footprint, blue versus green water and water use efficiency. At the first glance, the Alps can be considered as the ‘water tower of Europe’ with precipitation amount that are much higher than in semi-arid regions. However giving a closer look to the topographic conditions, irrigation management appears to be already an established practice over several decades in the steep-slope wine growing. Precise irrigation management seems to be of special importance for the vine growing under investigation. Furthermore, these mountain areas are expected to be affected more strongly from climate change with potentially higher water losses. This PhD thesis aimed to determine the occurrence of water stress under variable conditions between years under mountain conditions (Chapter 2), to address the physiological effects on grapevine under rainfall exclusion with repeated water stress cycles (Chapter 3) and to identify the impact of water stress and root chilling at the phenological stage of color change under semi-arid conditions (Chapter 4).  The work can be divided into 2 sections according to the study area were it was elaborated: South Tyrol, Italy (Chapter 2 and 3) and Washington State, USA (Chapter 4). The studies were carried out with a special focus in integrating vines physiological behavior to water stress to improve irrigation management. Plant water status was assess under field and semi-controlled conditions in two vine growing regions with different environmental conditions. The impact of the work consists in: Firstly, the evaluation of a new deficit irrigation approach under mountainous conditions with its impact on vines yield and quality over two years (Chapter 2). Secondly, in the deepening of the observed physiological plant responses from field to rainfall exclusion and repeated water stress (Chapter 3) and finally in the evaluation of water stress timing at probably the most important phenological stage of color change (veraison) with its involvement in hydraulic functioning of grapevines (Chapter4). The here obtained results confirm the validity of physiological tools as irrigation scheduling approach, highlight the importance of the integration of the phenological timing in the plant response to water stress assessment and increase the understanding of water stress within more variable environmental conditions. Our work found an up to now unknown connection between the water-stress release at the phenological stage veraison and the physiological ripening disorder berry shrivel.