Soil high Cd exacerbates the adverse impact of elevated O3 on Populus alba 'Berolinensis' L.

Pollution with both heavy metal and ground-level ozone (O3) has been steadily increasing, especially in the cities with heavy industry. Little information is known about their combined impacts on urban tree. This study was aimed at characterizing the interactive effects of soil cadmium (Cd) addition and O3 fumigation on visible injury and growth, photosynthesis, oxidative stress, antioxidant enzyme activities, abscisic acid (ABA) content and bioaccumulation of Cd in one-year-old Populus alba 'Berolinensis' saplings by using open top chambers in Shenyang city with developed heavy industry, Northeast China. In this study, poplar saplings were grown in the pots containing soil with different concentrations of Cd (0, 100 and 500 mg kg-1) under ambient air (40 µg L-1) and elevated O3 (120 µg L-1). The results showed that EO and its combination with high Cd (500 mg kg-1) induced significant foliar injury symptoms, decreased root weight (by 41.6%) and total biomass (by 17.4%), inhibited net photosynthetic rate and stomatal conductance, and increased malondialdehyde and ABA contents after 4 weeks of O3 exposure. Elevated O3 exacerbated the accumulation of Cd in leaves and stems of poplar plants grown in the pots with high Cd-polluted soil. Our results also indicated that high Cd pollution in soil increased the susceptibility of plants to O3 and exacerbated the adverse impact of elevated O3 on physiological metabolisms of poplar species, which implied that it was very necessary to take into consideration for O3-tolerance of tree species during phytoremediation of Cd-polluted soil in heavy industrial areas.