Chelant-Assisted Uptake and Accumulation of Cd by Poplar from Calcareous Arable Soils Around Baiyin Nonferrous Metal Smelters, Northern China

A pot experiment was used to examine the chelant-induced phytoextraction efficiency of poplar (Populus alba L. var. pyramidalis Bunge) for cadmium (Cd) from two severely contaminated calcareous arable soils originating from a mining and smelting region. The tested chelating agents were ethylenediamine tetraacetic acid (EDTA), ethylene glycol-(-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA), and citric acid (CA). The results showed that Cd mobilization remained constant in time for soils treated with EDTA and EGTA, whereas it decreased sharply in soils treated with CA. Additions of chelants caused leaf chlorosis and reduction in stem biomass on both soils under some treatments, whereas increased leaf biomass to some extent under all chelant treatments. EDTA and EGTA significantly increased the Cd concentration and amount in leaves on both soils (p < 0.05), with the highest leaf Cd concentration and amount reached 101.88 mg kg−1 and 1,760 µg pot−1 under EGTA treatments, respectively. The chelants significantly stimulated the translocation of Cd from poplar roots to leaves (p < 0.05), resulting in more than 70% of Cd amount in poplar shoots distributed in leaves under chelant treatments. However, the remediation factor is low (below 1%) due to the extremely high concentrations of Cd in the soil. Our results demonstrate that P. pyramidalis has high tolerance to Cd, but it is not suitable for a successful phytoextraction of Cd from severely contaminated arable soils. If P. pyramidalis is used for Cd phytostabilization, collections of leaf fall are required to avoid the recycling of leaf-bound Cd.