Grapevine plasticity and terroir: A multidisciplinary approach for dissecting the singular effect of soil on grapevine growth and berry quality

Grapevine (Vitis vinifera L.) is one of the most economically important fruit crops since it is largely used for wine production. It also represents the best paradigm for what concern phenotypic plasticity, meant as the capability of a single genotype to give rise to a range of different phenotypes. In fact, the complex interplay between a cultivar and the agri-environmental factors of a certain area, nowadays recognizable with the term terroir, has a crucial impact on grape traits that ultimately affects wine quality. Despite the high importance that scientists and traders give to the tipicity of each wine, not much is known about the singular effect that each terroir-factor has on the final product traits. To shed light on it, controlled experiments are needed for maintaining all the inputs as constant as possible, except one. In this research, we set an on-field experiment for studying the singular effect that soil – one of the main components of terroir – has on the grapevine growth and on the grape quality during two consecutive years by a multidisciplinary approach. Indeed, soil provides the grapevine with water and nutrients, but any chemical imbalance ends up influencing the vine growth and the quality of the grapes. Moreover, the influence of soil (regarding its texture, depth, mineral compositions, and microbiological community) has not been studied so widely, mainly due to its great variability even inside the same field. We chose three different soils from three Italian viticultural areas of Veneto region (Valpolicella, Valdobbiadene, and Legnaro), and set them in the same place but keeping them separated by means of cement boxes. Vitis vinifera cv. Corvina and cv. Glera were chosen for the study, hence exposing them to the same climatic and agronomical conditions. Specifically, we focused on the soil characterization by physico-chemical and microbiological analyses, and on phenological and physiological analysis of vines at both vegetative and reproductive stages. We also sampled berries throughout the maturation for metabolomic and transcriptomic analyses. The three soils differed from each other mainly by texture composition and the content of skeleton, organic matter, and potassium. Phenological differences emerged throughout years and between cultivars even if the effect of the soil was more evident considering the 2017 vintage. Plants grown in Valdobbiadene (VV) soil were delayed with respect to the others. This effect resulted less clear in 2018 vintage, possibly due to the interaction with the plant age and/or climate. Valpolicella (F) soil positively affected berry weight, whereas Valdobbiadene (VV) soil always produced lighter berries. In 2017, we also observed a stronger soil effect on the berry sugar accumulation pattern when compared to the latest vintage (2018). To study the molecular and biochemical plasticity, berries were collected in 2018 and processed for metabolomic and transcriptomic analyses. Transcriptomic analyses on both berry skin and pulp revealed a strong cultivar-tissue plasticity at harvest. Metabolomic analysis on berry skin revealed a significant effect of soil on several metabolites belonging to the phenylpropanoid pathway (especially flavonols and stilbenes) and high plasticity of metabolites accumulated in Corvina berry skin at harvest. Interestingly, the analysis revealed many interaction effect (cultivar*soil), especially for the class of flavan-3-ols, flavonolos, and hydroxycinnamic acids. Moreover, many different soil-metabolites correlations emerged when considering the two cultivars separately, suggesting, once again, a strong cultivar-specific response. This research can be meant as a first step in the study of the singular effect of the soil factor on grape traits, revealing its potential importance on the final product quality and supporting the hypothesis of a delicate balance which exists between a cultivar and its typical area of production.