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We assessed the effects of ambient tropospheric ozone on annual tree-ring growth, δ 13 C in the rings, leaf gas exchange and visible injury in three ozone-sensitive woody plant species in southern Switzerland. Seedlings of  Populus nigra  L.,  Viburnum lantana  L. and  Fraxinus excelsior  L. were exposed to charcoal-filtered air (CF) and non-filtered air (NF) in open-top chambers, and to ambient air (AA) in open plots during the 2001 and 2002 growing seasons. Ambient ozone exposures in the region were sufficient to cause visible foliar injury, early leaf senescence and premature leaf loss in all species. Ozone had significant negative effects on net photosynthesis and stomatal conductance in all species in 2002 and in  V. lantana  and  F. excelsior  in 2001. Water-use efficiency decreased and intercellular CO 2  concentrations increased in all species in response to ozone in 2002 only. The width and δ 13 C of the 2001 and 2002 growth rings were measured for all species at the end of the 2002 growing season. Compared with CF seedlings, mean ring width in the AA and NF  P. nigra  seedlings was reduced by 52 and 46%, respectively, in 2002, whereas in  V. lantana  and  F. excelsior , ring width showed no significant reductions in either year. Although δ 13 C was usually more negative in CF seedlings than in AA and NF seedlings, with the exception of  F. excelsior  in 2001, ozone effects on δ 13 C were significant only for  V. lantana  and  P. nigra  in 2001. Among species,  P. nigra  exhibited the greatest response to ozone for the measured parameters as well as the most severe foliar injury and was the only species to show a significant reduction in ring width in response to ozone exposure, despite significant negative ozone effects on leaf gas exchange and the development of visible foliar injury in  V. lantana  and  F. excelsior . Thus, significant ozone-induced effects at the leaf level did not correspond to reduced tree-ring growth or increased δ 13 C in all species, indicating that the timing of ozone exposure and severity of leaf-level responses may be important in determining the sensitivity of tree productivity to ozone exposure.

Ozone air pollution effects on tree-ring growth, δ 13 C, visible foliar injury and leaf gas exchange in three ozone-sensitive woody plant species