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Information on plant responses to combined ozone and cadmium stresses are scarce and limited to herbaceous species. In this research, two poplar clones (I-214 and Eridano), differently sensitive to O3, were grown for 5 weeks in pots supplied with 0, 53.5, and 160.5 mg(Cd) kg-1 (soil d.m.) and then exposed to 15-d O3 fumigation (0.06 mm3 dm-3, 5 h a day). The effects of the two stressors, alone or in combination, on Cd, Ca, Fe, and Zn accumulation in above-nad below-ground organs, photosynthesis, leaf pigments, and accumulation of H2O2 and NO were investigated. Cadmium induced a reduction in stomatal conductance and a significant accumulation of H2O2 and NO in both clones nad negatively affected the carotenoid content in I-214. Ozone, on the other hand, counteracted Cd accumulation in the above-ground organs and significantly increased the xanthophyll de-epoxidation state indicating photoinhibition in O3-treated plants. Surprisingly, O3 alone or in combination with Cd decreased H2O2 accumulation in I-214. The NO production was generally stimulated by Cd, whereas it decreased following O3 exposure in I-214. The overall data indicate that Cd and O3 induced clone specific responses. Moreover, when they were applied in combination, antagonistic rather than synergistic effects were observed. |
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