Tree-ring isotopic study reveals a different degree of tolerance to summer stress conditions in olive tree cultivars

Recent studies have indicated that for every degree of global warming, mean precipitation will likely decrease by about 4% in many regions, particularly in the southern Mediterranean areas (Vinci et al., 2023a). Among the constituents of summer stress, drought and high temperatures are usually the most critical. Olive (Olea europaea L.) is a Mediterranean sclerophyll tree species known for its relatively high tolerance to drought (Portarena et al., 2024). However, among olive cultivars, there are significant genetic and phenotypic plasticity differences in responses to climate-related stresses (Brito et al., 2019). Data that comprehensively assesses how different olive cultivars respond to climate variability, in comparison with agronomic and productive data, are scarce. Carbon stable isotopes in tree rings can be used to identify long-term adjustments in tree gas-exchange processes (Roden and Farquhar, 2012). The main objectives of this study were to determine, in young olive trees from two high-quality Italian cultivars, ‘Maurino’ and ‘Moraiolo’, the inter- annual dynamics of δ13C in earlywood and latewood over three years, and to examine the relationships between photosynthetic performance and agronomic traits.