Abstract
We compared leaf visible injury and physiological responses (gas exchange and chlorophyll a fluorescence) to high O3 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 O3 exposure. Onset and extent of visible foliar injury suggested that F. excelsior was more O3 sensitive than F. ornus. The higher stomatal conductance in F. ornus than in F. excelsior suggested a larger potential O3 uptake, in disagreement to lower visible foliar injury. The higher carbon assimilation in F. ornus suggested a higher potential of O3 detoxification and/or repair. Contrasting geographical variations of ash sensitivity to O3 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.
Highlights
Tropospheric ozone (O3) is regarded as one of the most widespread air pollutants[1]
Onset and extent of visible foliar injury as well as faster decline in photosynthesis suggested that F. excelsior was more sensitive to O3 than F. ornus
Gas exchange and chlorophyll a fluorescence measurements showed that O3 affected photosynthetic performances
Summary
Tropospheric ozone (O3) is regarded as one of the most widespread air pollutants[1]. Current O3 levels in Europe are potentially high enough to adversely affect forests[1]. Tree species exhibit a wide range of sensitivity, even at the intraspecific level[2,3,4,5,6,7]. Degree and type of invisible and visible O3 foliar injuries depend on several plant factors: stomatal conductance, leaf morphological features, apoplastic detoxification, and the response that plants are able to activate[8,9]. These factors are strongly dependent on genotype and on the ecological strategies that plants adopt to avoid or tolerate O3 stress
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