Exploring the grapevine metabolic plasticity under drought

Grapevine is a highly adaptive liana that is cultivated in a wide diverse range of climates worldwide. Nevertheless, climate change is threatening the sustainability of viticulture in several regions where stress events such as drought and heat waves are negatively influencing yield, grape composition, wine quality and vine health. Several studies addressed the effect of single stressors on the vine metabolism and grape composition. However, limited information is available on the interaction between water availability and other weather specific parameters such as light and temperature. Most of the information we currently have on such interactions come from indirect measurements. The few research that directly addressed the issue was performed in glasshouses or growing chambers, on small plants grown in small pots; moreover, composition parameters analysed were very few. Our project entitled Exploring the grapevine metabolic plasticity under drought (PlasticGrape) aims to fill this gap by studying the interactive effects of drought stress and other climatic variables (such as light and temperature) on the plant physiology and fruit metabolism. The PlasticGrape project is ambitious and to achieve its objectives a unique experimental design that was never implemented for any other crop before will be carried out. Such design includes the use of a set of 160 grapevines (cv. Pinot noir), planted and developed in one single environment then split in two different locations characterized by different climates (Tulln, Austria and Vipava, Slovenia). In both locations, mirrored water deficit treatments will be performed with the aim to study the interactive effects of water stress and climate on the plant physiology and metabolome. Complementary experiments will be carried out in greenhouse conditions as well. The metabolite profiling of leaves and berries will allow to comprehensively characterizing the alterations of primary and secondary metabolism. Comprehensive analyses of grapevine metabolome will help to elucidate changes in leaf and berry metabolism as an adoption response to drought and specific climatic conditions.

The PlasticGrape project investigated the plasticity (i.e. the ability of an organism to change in response to different environment) of grapevine in response to drought under different climatic scenarios. The project aim was to understand how the response of the same grapevine genotype to drought could change when under cooler or warmer climatic conditions. The project focused on plant ecophysiology parameters and leaf and berry metabolism as main response variables, while considering also agronomic parameters such as yield and plant growth. The project unique experimental design consisted in the setup of mirrored water deficit treatments conducted in two different sites (Tulln-Austria and Vipava-Slovenia, cooler and warmer, respectively) while using a genetically uniform cohort of plants (cv. Pinot noir grafted on SO4 rootstock). Furthermore, experiments under controlled climatic conditions in greenhouse chambers maintained at different temperature regimes were conducted to better disentangle the interaction of drought x temperature effects on the plant responses. Along the different experimental setups, leaves and berries were sampled and analysed for primary and secondary metabolites as well as gene expression. Heat accumulation was higher in Vipava than in Tulln during the two years of experiments performed, resulting in higher water demand and transpiration, but also a general anticipated phenology. Agronomically, some important parameters were impacted such as the leaf area/fruit ratio (that was higher in Tulln than in Vipava), but also berry ripening: while sugar concentration was similar being the main parameter to decide harvest, acidity was lower and pH higher in the warmer Vipava as compared to Tulln confirming general trends among cool and warm climate viticulture. The chemical analyses of leaves and berries also highlighted the impact of climatic factors on the plant metabolism, showing that the main differences among samples could be separated according to the location of the experiment irrespective of sampling time and water deficit treatment. This trend was particularly noticeable when analyzing grape berry and leave volatile compounds as terpenoids, whereas primary metabolites (minor sugars, organic acids and amino acids) were influenced by climate to a smaller extent. While water deficit impacted several primary metabolites and phenolics, only few of those compounds were consistently influenced in the two locations across the two vintages. This suggests that the metabolic response of grapevine leaves and berries to water constraints is complex and specific. On the other hand, grapevine metabolic response to temperature seems to be wider and more consistent. This observation was confirmed by the greenhouse experiments, where combinations of different temperatures and water treatments were imposed. Similarly to what observed between two locations (Vipava & Tulln), temperature was the most significant driver of changes observed at the metabolic level and in some instances overcame the effect of imposed water deficit.