Integrating leaf morphological traits can improve the predictive capacity of flux-based ozone metrics for ecophysiological responses in ornamental plant species

Ozone (O3) is a seasonal gaseous pollutant with a strong oxidizing effect on vegetation. In this study, photosynthesis (An), stomatal conductance (gs), dark respiration (Rd), relative chlorophyll content (SPAD), and fluorescence (Fv/Fm) were recorded for 15 ornamental species during O3 Free-Air Controlled Exposure (O3-FACE) experiments carried out in central Italy, to assess the ecophysiological response to O3 stress. The exposure- and flux-based O3 metrics (AOT40 and POD1, respectively) were calculated, as well as the Leaf Index Flux (LIF), an innovative species-specific O3 index obtained by the ratio of POD1 to Leaf Mass per Area (LMA). The gs Jarvis model was parameterized and LMA was collected for all the species. The three metrics were correlated with the ecophysiological parameters, and linear models were used to assess their predictive potential. Results indicated that LIF showed the strongest statistically significant correlation with An, Rd, and Fv/Fm compared to POD1 and AOT40. Moreover, LIF had a stronger explanatory power for all ecophysiological parameters when species-specific differences were considered. Therefore, the present study highlights the novelty of combining leaf physiology and morphology in O3 metrics. This supports a wider adoption of LIF, rather than POD1 and AOT40, to obtain more reliable results for O3 risk.