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

Abstract

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). Plants of S. alfredii were grown for 60 days in nutrient solution with 100 μmol 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. In the hydroponic experiment, both low ( 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. 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.