Multiscale assessment of ozone impacts on woody species integrating ecophysiological and structural–functional responses across field and free-air experimental conditions

Tropospheric ozone (O₃) is a widespread phytotoxic pollutant that constrains plant physiological performance, alters carbon allocation patterns, and threatens forest functioning under current and future atmospheric scenarios. This dissertation develops an integrated, multi-scale framework to quantify O₃ effects on woody species by combining controlled fumigation experiments, trait-based modeling, long-term field observations, and high-resolution growth analyses. Free-Air Controlled Exposure (FACE) experiments on ornamental and forest species show that flux-based metrics outperform concentration-based indices in predicting ecophysiological responses. In particular, the Leaf Index Flux (LIF), which integrates stomatal O₃ uptake (POD₁) with leaf structural investment (leaf mass per area), consistently shows higher explanatory power for photosynthesis, respiration, chlorophyll status, and photochemical efficiency, highlighting the importance of coupling physiological fluxes with morphological traits in O₃ risk metrics. Experiments on Robinia pseudoacacia further demonstrate that rhizobial symbiosis mitigates O₃ injury by reducing stomatal O₃ uptake and buffering biomass losses, resulting in higher critical levels compared to O₃-sensitive species. Across a broader range of woody taxa, O₃- induced biomass reductions are species and functional type-dependent, with belowground compartments showing the highest sensitivity, suggesting that O₃ affects not only total carbon accumulation, but also its distribution among plant organs. Field-based assessments integrating sap flow measurements refine stomatal flux estimates and improve the prediction of O₃-visible foliar injury, supporting the revision of critical levels using in situ physiological data. Finally, high-frequency dendrometric analyses coupled with rolling partial-correlation approaches indicate that dendrometric time series can be effectively used to explore short, sub-monthly periods during which O₃ exposure may be associated with variations in irreversible radial growth. These associations emerge primarily at fine temporal scales and tend to be progressively attenuated when growth and O₃ signals are aggregated over longer windows. Overall, this study highlights the potential of integrating site-specific O₃ flux estimates with high-resolution dendrometric data to improve the interpretation of O₃–growth relationships in mature Mediterranean beech forests. This work supports the adoption of physiologically-based, flux-based, and temporally-explicit frameworks as a robust basis for improving O₃ risk assessment in forest ecosystems.