Correspondence between physiological plant variables and carbon isotope composition in different climate winegrape regions

Abstract

Context and purpose of the study – The climate is the environmental factor that contributes with greater weight in the variability of the yield and the composition of the grape, therefore, it is key in the determination of the typicity of the product. Of the environmental factors, the evolution of water availability conditions, among other things, the biochemical evolution of the compounds of the grape and the type of wine to be elaborated. An integrating parameter of the hydric state of the plant is the carbon isotopic composition (δ13C). This indicator is a useful parameter to characterize the water status during the maturation period and estimate the transpiration efficiency or water use efficiency (EUA) in the vine. The aim of this study was to evaluate the ability of δ13C to differentiate wine growing regions of Uruguay by the relationship between the isotope indicator and the main productive variables.

Material and methods – The study was conducted in 2018 in commercial vineyards of the Tannat variety grafted on to SO4 rootstock, trained in a trellis system. The vines were planted in a four different climate regions for Uruguay determined by Multicriterial Classification system (MCC): 1-IH5, IF2, IS1-Salto (North, corresponds to a warm climate, cool nights and moderate drought), 2- IH4, IF2, IS1-Durazno (Center, corresponds toa temperate-warm climate, nights and moderate drought), 3- IH4, IF1, IS1-Colonia (Northwest, corresponds to a temperate-warm climate, warm nights, moderate drought), and 4- IH3, IF2,IS1-Canelones (South corresponds to a temperate climate, cool nights and moderate drought). Climatic data were obtained from meteorological stations in each region according to World Meteorological Otganization (WMO standards). For each climatic region, the state hydric of the plant (ψb) was determined in four moments in the cycle; at harvest: berry weight, free amino nitrogen in must, δ13C in berries, pH, acidity, sugars and total and extractable anthocyanins it was determined.

Results – In the studied zones, under rainfed conditions, the values of δ13C were correlated to the water deficit. The δ13C was strongly correlated with the hydric state of the plant and allowed to differentiate the two most extreme climatic regions (1 and 4). The most negative δ13C values were obtained in climatic zone 1 (warm), explained by the rainfall accumulated during the maturation period. The δ13C showed significant correlations with the weight of the berry for each of the zones, free amino nitrogen in the berry, total and extractable anthocyanins, and the total acidity. These results indicate that δ13C, is an interesting indicator to evaluate the quality of the grape and confirm climatic regions.