Influence of pH on the Particulate-Bound Cd Speciation and Uptake by Plants

The speciation of heavy metals in soil is a better indicator for assessing the bioavailability than the total concentration. Soil pH is a vital factor influencing the particulate-bound metal speciation and the metal dynamics at rhizosphere soil-root interface. In this study, greenhouse pot experiment was conducted to reveal the influence of pH on the speciation of cadmium (Cd) in solid phase of soil and the amount of Cd uptake by different ecotype plants. The results illustrated that the exchangeable Cd decreased obviously with the increase of soil pH, while the residual Cd displayed the reverse. The amount of Cd uptake by plants increased with pH decreased, and pH 5.5 exhibited the optimum for plants growth and metal uptake. Furthermore, the biomass and uptake capability of the hyperaccumulator plants (Sedum alfredii and Beta vulgaris var. cicla L with red leaves) were higher than the corresponding non-hyperaccumulator plants. Results indicated that the pH decrease and rhizosphere effects of hyperaccumulator could facilitate the activation of Cd and enhance the phytoremediation efficiency significantly.