Visible Foliar Injury and Physiological Responses to Ozone in Italian Provenances of Fraxinus excelsior and F. ornus

We compared leaf visible injury and physiological responses (gas exchange and chlorophyll a fluorescence) to high O(3) exposure (150 nmol mol(–1) h, 8 h day(–1), 35–40 days) of two woody species of the same genus with different ecological features: the mesophilic green ash (Fraxinus excelsior) and the xerotolerant manna ash (F. ornus). We also studied how provenances from northern (Piedmont) and central (Tuscany) Italy, within the two species, responded to O(3) exposure. Onset and extent of visible foliar injury suggested that F. excelsior was more O(3) sensitive than F. ornus. The higher stomatal conductance in F. ornus than in F. excelsior suggested a larger potential O(3) uptake, in disagreement to lower visible foliar injury. The higher carbon assimilation in F. ornus suggested a higher potential of O(3) detoxification and/or repair. Contrasting geographical variations of ash sensitivity to O(3) were recorded, as Piedmont provenances reduced gas exchange less than Tuscan provenances in F. excelsior and more in F. ornus. Visible injury was earlier and more severe in F. excelsior from Piedmont than from Tuscany, while the provenance did not affect visible injury onset and extent in F. ornus.