The Effect of Increasing Irrigation Rates on the Carbon Isotope Discrimination of Apple Leaves

13C discrimination (Δ13C) has been used in research as an indicator of water availability crops; however, few data are available concerning fruit trees. The aim this study was to examine the effect irrigation on Δ13C values apple leaves. We assumed that would increase with intensity. trees (Malus domestica) cv. ‘Red Jonaprince’ determined years 2019–2022. Leaf samples were collected spring, June, at beginning campaign, and autumn, September, following harvest. doses applied replenish consumption, 0% (ET0), 50% (ET50), 75% (ET75), 100% (ET100), calculated evapotranspiration (ET) levels. In November, leaves from different positions shoots sampled, assuming signature reflect changes occurring supply during their growth. rates had a significant when for spring summer months pooled. On average, increased 20.77‰ 20.73‰ ET0 ET50, respectively, 20.80‰ 20.95‰ ET75 ET100, respectively. When obtained analysed separately, weak (p < 0.043). value always higher treatment ET100 than ET0, individual experimental terms; differences minor mostly insignificant. leaf position strong Δ13C; gradually decreased growing two-years-old branches (22.50‰) youngest top current year’s (21.07‰). This order similar all years. results experiment suggest apples is affected not only by growth, but also use C absorbed previous