Influence of nitrate fertilization on Hg uptake and oxidative stress parameters in alfalfa plants cultivated in a Hg-polluted soil

The mineral nutrition status of plants might affect the accumulation of heavy metals, which in turn could be reflected in altered plant sensitivity. Very little information is available about the effect of the nitrogen nutritional status on mercury (Hg) toxicity. We compared physiological stress parameters sensitive to Hg in alfalfa (Medicago sativa) plants grown in Hg-polluted soils that were amended with two different fertilizers: without NO3− (PK) or with NO3− (NPK). Several parameters of oxidative stress, such as antioxidative enzymatic activities, lipid peroxidation, and chlorophyll content were analysed. The study was carried out in a green house with soil from an agricultural land plot located in Almadén (Spain), which contained an average Hg concentration of 12.4 mg kg−1, most of it found mainly as cinnabar (HgS). Our results suggest that nitrogen supply prevents oxidative stress in roots, but may improve root development and increase the uptake of Hg from the soil above safety consumption limits. This work highlights the importance of proper nitrogen fertilization towards future phytoremediation applications with alfalfa plants.

► Alfalfa plants were grown in a Hg-polluted soil an fertilized with or without NO3−.
► Oxidative stress parameters sensitive to Hg were measured.
► Plants given NO3− (NPK) were less stressed than those fertilized without NO3− (PK).
► Interestingly, plants supplied with NO3− accumulated more Hg.
► Albeit positive for plant tolerance in low N soils, NPK fertilization mobilized Hg.