Estimating cadmium availability to the hyperaccumulator Sedum plumbizincicola in a wide range of soil types using a piecewise function.

Estimating the bioavailability and predicting the uptake of metals to hyperaccumulators is very important in developing the field application of phytoextraction. A pot experiment was conducted using 108 agricultural soils covering a wide range of soil properties by the cadmium (Cd) hyperaccumulator Sedum plumbizincicola . The contributions of a range of soil properties to Cd uptake were quantified. Soil total, soluble, CaCl 2 -extractable and diffusive gradients in thin films (DGT)-extractable Cd concentrations (Cd total , Cd soln , Cd CaCl 2 and Cd DGT ) were used to estimate Cd bioavailability and predict shoot Cd concentration (Cd shoot ) using a piecewise function. Cd total and pH were the two major contributors to Cd uptake. Cd shoot showed a logarithmic increase with Cd total from 0.30 to 10.0 mg kg −1 but no further increase when Cd levels exceeded 10 mg kg −1 . Soil pH had a discernible negative effect on Cd bioavailability from pH 5.5 to 7.5 but a weak influence at pH < 5.5 or pH > 7.5. This indicates that the optimum pH for phytoextraction with S . plumbizincicola was ~5.5 and lower pH produced little increase in shoot Cd uptake. DGT gave the best estimation of Cd bioavailability across all the data. When Cd total  > 10 mg kg −1 , none of the four measures was accurate enough to predict Cd shoot but when pH > 7.5 all the four measures were well correlated with Cd shoot . Piecewise equations in different ranges of Cd total or pH significantly improved the prediction of Cd shoot compared with the global equations derived from all the data. Compared with the piecewise equations, when pH > 7.5 Cd shoot was greatly overestimated with the global equation of Cd total . Our study provides useful information on the soils in which phytoextraction with S . plumbizincicola is feasible in the field. Capsule Cd availability to S . plumbizincicola was estimated by a piecewise function in soils with wide ranges of total Cd concentration and pH. [ABSTRACT FROM AUTHOR]