Nitrogen fertilizer enhances zinc and cadmium uptake by hyperaccumulator Sedum alfredii Hance

Purpose Nitrogen (N) fertilization is known to have a substantial effect on heavy metal uptake in plants. However, the impact of N fertilization on plant growth and heavy metal uptake of hyperaccumulator plants remains unclear. This study examined the effect of N fertilization on growth and uptake of zinc (Zn) and cadmium (Cd) in Zn/Cd-hyperaccumulating plants species, Sedum alfredii (S. alfredii) Hance (Crassulaceae). Materials and methods Plants of S. alfredii were grown for 60 days in nutrient solution with 100 mu mol Cd L-1 and 0-10 mmol N L-1, and in a Cd-contaminated soil receiving N fertilizer and composted pig manure amendment. Biomass production, nutrient uptake, and concentrations and accumulation of Zn and Cd in plant parts were measured. Results and discussion In the hydroponic experiment, both low (< 1 mmol L-1) and high (> 5 mmol L-1) N supply decreased the growth and Zn and Cd accumulation in the whole plants. The 2.5 mmol N L-1 is an optimal N dosage for shoot biomass production and Zn accumulation in shoots, while the 1.0 mmol N L-1 is an optimal N dosage for Cd accumulation in shoots, which was 68.1% higher than the control. The N doses of 1 to 2.5 mmol L-1 N represented optimal conditions for Zn and Cd accumulation in the shoots of S. alfredii seedlings. In the soil pot experiment, shoot dry weight decreased with increasing N fertilization rate, while composted pig manure decreased biomass production. Both Zn and Cd accumulation in the shoots of S. alfredii decreased along with the addition of higher N fertilization rate. However, the composted pig manure amendment increased the accumulation of Zn, but not Cd in the shoots. Conclusions The application of N at appropriate amount enhanced the phytoremediation efficiency by S. alfredii in Zn/Cd polluted fields, but the effectiveness of phytoextraction technology needs to be validated in the field trials.