Three years of exposure to lead and elevated CO2 affects lead accumulation and leaf defenses in Robinia pseudoacacia L. seedlings

Few studies have explored the long-term effects of elevated atmospheric CO 2 combined with lead (Pb) contamination on plants. The objective of this study was to examine the effects of 3 years of elevated CO 2 (700 ± 23 μmol mol –1 ) on Pb accumulation and plant defenses in leaves of Robinia pseudoacacia L. seedlings in exposed to Pb (500 mg kg −1 soil). Elevated CO 2 increased Pb accumulation in leaves and Pb removal rate in soils. In plants exposed to Pb stress, total chlorophyll and carotenoid contents in leaves were lower under elevated CO 2 than under ambient CO 2 , but seedling height and width increased under elevated CO 2 relative to ambient CO 2 . Elevated CO 2 significantly ( p  < .01) stimulated malondialdehyde content in leaves under Pb exposure. Superoxide dismutase and catalase activity increased significantly ( p  < .01), peroxidase activity decreased significantly ( p  < .01), and glutathione , cystine, and phytochelatin contents increased under elevated CO 2  + Pb relative to Pb alone. Elevated CO 2 stimulated the production of soluble sugars, proline, flavonoids , saponins, and phenolics in plants exposed to Pb stress. Ove rall, long-term elevation of CO 2 increased Pb-induced oxidative damage in seedlings, but enhanced the phytoextraction of Pb from contaminated soils.