Growth Responses and Metal Accumulation in an Ornamental Plant (Osmanthus fragrans var. thunbergii) Submitted to Different Cd Levels

To characterize the effects of Cd supplies on the accumulation efficiency of Cd, Pb, Zn, and Cu in an ornamental plant (osmanthus, Osmanthus fragrans var. thunbergii), a pot experiment using current-year osmanthus in field was carried out in western China. Biomass and its components showed a decreasing tendency as Cd supply increased, though insignificant differences were observed between treatments with a low and no Cd supply. Cd supplies increased the concentrations of Cd and Pb in plants, but the concentrations of Zn and Cu in plant showed a decreasing tendency with the increase of Cd supplies. Cd supplies also increased Cd accumulation for the plant, although the highest Cd accumulation was observed at a low Cd supply (T1). A higher Pb accumulation in the osmanthus was also detected in T1 than the other treatments. However, Zn and Cu accumulations decreased with the increase of Cd supplies. The examined osmanthus showed relative higher Cd and Pb transfer efficiencies in the presence of Cd supplies, but Cd supplies can limit the transfer of Zn and Cu. The results suggested that the examined osmanthus has potential for use in metal-contaminated environments due to phytoremediation application in the soil. 1. Introduction One of the main environmental problems in many developing countries is the increasing pollution by toxic metals related to increased industrial activity and the heavy use of chemical fertilizer, pesticides, and herbicides in agriculture [1–3]. Bioaccumulation of toxic metals in humans can result in several harmful symptoms in gastrointestinal, neurological, and immunological systems [4, 5]. The most dangerous metals include the so-called “toxic trio”: Cd, Pb, and Hg, for which no biological function has been found [6–8]. Besides them, there is a long list of other metals which although essential in low doses, become toxic in high doses, such as Zn, Cu, and Mn [5]. Many soils are receiving lots of toxic metals with high pollution, but many others only display pollution with one or two metal. Compared with other toxic metals, Cd is not an essential nutrient in higher plants, and the exposure to relatively low concentrations results in high toxicity to plants and animals [9]. Unfortunately, Cd is the most common toxic metal in many areas worldwide. Since Cd stress often decreases plant growth [10], exposure to Cd can decrease accumulation of other toxic metals (such as Pb, Zn, and Cu) in plants. Moreover, the study on tobacco found that there were negative correlations as Cd accumulation increased, Zn accumulation decreased, implying