Nitrogen isotope ratio from soil to wine: an initial approach in viticulture and oenology

Stable isotope ratio analysis of so-called bioelements (H, C, N, O, S) is used for food authenticity control and to verify the geographical origin of food products (Kelly et al., 2005). One of the most well-known fields of application is analysis of the 2H/1H and 13C/12C ratios of wine ethanol and the 18O/16O of wine water to check whether sugar and water have been added and to verify the origin declared on the label (Dordevic et al., 2012). The 15N/14N ratio has been measured in several foods to trace geographical origin and agricultural systems (Kellyet al., 2005), but not in wine. This study follows the 15N/14N ratio (expressed as d15N) through the soil-vine-leaf-grape-wine chain in different vineyards located in the province of Trento and Modena, in order to measure the variability of this ratio through the different matrices and understand the influence of physiological mechanisms and vinification processes on the nitrogen isotope value. Nitrogen in grape juices comes from the soil through plants, so its ä15N value is influenced by the external nitrogen source. The d15N of a plant is related to that of its N sources and theä15Nsource is the mean of the ä15N values of all potential N sources, weighted by their availability (Robinsonet al., 2001). The variability of d15N in the soil was studied at two different depths, and leaves and grape samples were collected from grapevines grown in proximity to the sampled holes in the soil. Some of the juices were inoculated with 9 different selected dry yeasts according to the manufacturer’s specifications, and microvinified using different N-based activants. The data showed that the soils were homogeneous; d15N did not change according to depth. The d15N values of leaves and branches showed the same trend as the soils; however, they were more negative, due to N isotope fractionation during assimilation and physiological mechanisms within the plant (Evanset al., 2001). The results obtained by analysing grape juices before and after fermentation demonstrated that the d15N of must and wine conserved the same trend observed in soil and vine, being slightly higher than in leaves and branches