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.
(Copyright © 2018. Published by Elsevier B.V.)