Fertilizer amendment for improving the phytoextraction of cadmium by a hyperaccumulator Rorippa globosa (Turcz.) Thell

Two main pathways of phytoremediation of heavy metal-contaminated soils are phytostabilization and phytoextraction. Some soil amendments can strengthen phytostabilization or phytoextraction through either reducing heavy metal bioavailability in soil or increasing the heavy metal accumulation capacity of the hyperaccumulator (enhancing heavy metal concentration or shoot biomass of the hyperaccumulator). Urea and chicken manure are often used as fertilizers. This research will explore their effects on a newly found hyperaccumulator, Rorippa globosa (Turcz.) Thell., phytoremediating cadmium (Cd). Pot culture experiment was conducted to study the accumulation characteristics of R. globosa at different Cd contamination concentrations under one fertilizer level (1 g kg(-1) for urea and 100 g kg(-1) for chicken manure), as well as the same Cd dose (20 mg kg(-1)) under different fertilizer doses. Cd was artificially spiked at 2.5, 5, 10, and 20 mg kg(-1). Urea was amended at 0.5, 1, and 2 g kg(-1), while chicken manure was supplemented at 50, 100, and 200 g kg(-1). The heavy metal concentration in soil and plant samples was determined using an atomic absorption spectrophotometer. pH, N, P, K, and so on in soil samples were determined by normal method. The results showed that urea application did not affect the Cd concentrations in root, stem, leaf, inflorescence, and shoot of R. globosa, but chicken manure significantly decreased (p < 0.05) them by 28.4%, 29.3%, 30.8%, 24.9%, and 28.3%, respectively, owing to decreased extractable Cd in soil. Thus, strengthening the capacity (Cd accumulation in plant shoot, micrograms per pot) of urea was higher than that of chicken manure, though both shoot biomasses increased by one to threefold. Furthermore, the addition of urea and chicken manure increased the organic material, nitrogen, phosphorus and potassium, the microorganism count, urease, and the phosphatase activities of soil, indicating their eco-friendly function. Urea is ideal for optimizing phytoextraction of Cd using R. globosa, while chicken manure is appropriate for phytostabilization. Although chicken manure addition significantly increased (p < 0.05) Cd extraction capacity (micrograms per pot) of R. globosa, extractable Cd concentration in soil was significantly decreased (p < 0.05). In contrast, urea addition had no impact on soil extractable Cd and significantly increased Cd extraction capacity (micrograms per pot) of R. globosa by growth stimulation. Thus, this study demonstrates the effect of fertilizer amendment in enhancing phytoextraction using a Cd hyperaccumulator, R. globosa, only by increased plant biomasses. Furthermore, chicken manure can strengthen phytostabilization because it decreased extractable Cd in soil.