Hydrogen and Oxygen Isotope Fractionation Effects in Different Organ Tissues of Grapes under Drought Conditions

A study of different grapevine tissues and organs (root, stem, leaf, fruit) water isotope fractionation models from high-quality wine grapes produced in the Helan Mountains, a key wine-producing area in northwestern China, was undertaken. Results showed that δ²H values of local groundwater sources were more negative than rivers and precipitation. Soil water δ²H and δ¹⁸O values were significantly higher than those of other environmental water sources. Water from the soil surface layer (0-30 cm, δ²H and δ¹⁸O values) was more positive than the deeper layer (30-60 cm), indicating that soil water has undergone a positive fractionation effect. δ²H and δ¹⁸O values of tissues and organs from different grape varieties followed a similar pattern but were more negative than the local atmospheric precipitation line (slope between 4.1 to 5.2). The ²H and ¹⁸O fractionation relationship in grapevine organs was similar, and ¹⁸O has a higher fractionation effect than ²H. δ²H and δ¹⁸O values showed a strong fractionation effect during the transportation of water to different grape organs (trend of stem > fruit > leaf). This study showed that ^18/16O fractionation in grapes is more likely to occur under drought conditions and provides a theoretical basis to improve traceability accuracy and origin protection of wine production areas.