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Tropospheric ozone (O₃) is a detrimental air pollutant causing phytotoxic effects. Several O₃ indices are used to assess the risk for vegetation, e.g., the exposure-based AOT40 (accumulated ozone exposure over a threshold of 40 ppb) and the stomatal-flux based POD₁ (Phytotoxic Ozone Dose above a threshold of 1 nmol m⁻² s⁻¹). Leaf Mass per Area (LMA) is recommended as a simple index to explain the plant tolerance capacity to O₃. We therefore tested a new species-specific O₃ index (Leaf Index Flux—LIF: calculated as stomatal O₃ flux/LMA) as a proxy of the avoidance/tolerance capacity against O₃ stress according to datasets of visible foliar injury (VFI) in forest monitoring and a manipulative Free-Air Controlled Exposure (FACE) experiment. For the forest monitoring, AOT40, POD₁, and LIF were calculated from hourly O₃, soil moisture, and meteorological measurements at nine Italian forest sites over the period 2018–2022. The results were tested for correlation with the O₃ VFI annually surveyed at the same sites along the forest edge (LESS) or inside the forest (ITP) and expressed as relative frequency of symptomatic species in the LESS (SS_LESS) and Plant Injury Index per tree in the plot (PII_ITP). Based on VFI occurrence at ITP and LESS, Fagus sylvatica was considered the most O₃-sensitive species, whereas conifers (Pinus pinea and Picea abies) and other deciduous/evergreen broadleaf (Quercus petraea, Q. cerris, Q. ilex, and Phyllirea latifolia) showed rare and no O₃ VFI. Shrub species such as Rubus spp. and Vaccinium myrtillus were O₃-sensitive, as they showed VFI along the LESS. AOT40 did not show significant correlations with the VFI parameters, POD₁ increased with increasing SS_LESS (p = 0.005, r = 0.37) and PII_ITP (p < 0.001, r = 0.53), and LIF showed an even higher correlation with SS%_LESS (p < 0.001, r = 0.63) and PII_ITP (p < 0.001, r = 0.87). In the FACE experiment, PII was investigated for five deciduous and three evergreen tree species following one growing season of exposure to ambient and above-ambient O₃ levels (PII_FACE). Moreover, PII_FACE resulted better correlated with LIF (r = 0.67, p < 0.001) than with POD₁ (r = 0.58, p = 0.003) and AOT40 (r = 0.35, p = 0.09). Therefore, LIF is recommended as a promising index for evaluating O₃ VFI on forest woody species and stresses high O₃ risk potential for forest species with high stomatal conductance and thin leaves. Full article

Mediterranean plants biosynthesize high amounts of polyphenols, which are important health-promoting compounds. Leaf polyphenolic composition changes according to environmental conditions. Therefore, it is crucial to know the temporal variation in their production. This study aimed to: i) evaluate the monthly and daily changes in polyphenols of Phyllirea latifolia, Cistus incanus, and Pistacia lentiscus to identify their best harvesting moment, ii) verify the possible correlations between phenolic production and temperature and irradiation, iii) evaluate their antioxidant capacity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radical (OH)scavenging assays. The extracts of leaves harvested at 8:00, 13:00 and 18:00, in May, July, and October for two years were analysed by HPLC-DAD. Both “month” and “time of the day” affected the polyphenolic content in all species. July at 13:00 was the best harvesting moment for all polyphenolic classes of P. latifolia and only for some classes of C. incanus and P. lentiscus. Environmental parameters positively correlated with the polyphenols of C. incanus and P. latifolia, while the antioxidant capacity only varied in this last species, reaching the highest value in July. Results of the study allow to determine the balsamic time for each species. Moreover, the relationship between polyphenols and environmental data can be useful for the cultivation of these plants under controlled conditions. Full article