Photosynthetic behaviour of two Italian clones of European beech (Fagus sylvatica L.) exposed to ozone.

Two Fagus sylvatica clones, one from central and the other from southern Italy, were exposed to charcoal-filtered or ozone-enriched (150 ppb, 5 h d-1) air for 14 days. Leaf gas exchange, chlorophyll a fluorescence, leaf greenness and maximum RuBP-saturated rate of carboxylation have been measured. Even though the two clones came from sites with different environmental features, their photosynthetic performances were similarly depressed by fumigation, apart from stomatal conductance. An uncoupling between stomatal conductance and carbon assimilation was assumed to take place. Mesophyllic limitations were likely to be the most limiting factor. Photosynthetic light reactions (i.e. apparent electron transport rate) responded to ozone earlier than dark reactions (i.e. maximum RuBP-saturated rate of carboxylation)