D. Di Baccio

Leaf structural modifications in Populus × euramericana subjected to Zn excess

In previous experiments elevated but sub-symptomatic applications of Zn (0.1 mM and 1 mM) caused impairments in growth parameters and photosynthetic performance of Populus × euramericana (Dode) Guinier clone I-214. The aim of this work was to evaluate leaf morphological and anatomical traits in this clone in response to the same Zn concentrations. The results showed that Zn treatments induced variations in leaf dry mass, area, mesophyll thickness, intercellular spaces, stomatal density and size. Stronger modifications, especially concerning stomata characteristics induced by 1 mM Zn, were consistent with physiological impairments while those induced by 0.1 mM Zn suggested a compensatory strategy for maintaining functional integrity.

Differential ozone sensitivity interferes with cadmium stress in poplar clones.

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.