Cd (cadmium) is one part of natural components in the Earth crust. When artificial activities intensify, it then accumulates a lot and causes soil contamination, and ultimately be absorbed through the food chain and poses a health threat to animals and humans.

Solanum nigrum L. a newfashioned Cd hyperaccumulator, shows a potential for bio-accumulating Cd in contaminated soil with the addition of N fertilizer.

However, few studies have affirmed that which one or two N fertilizer at a special concentration induced the highest Cd phytoextraction efficiency and the strongest Cd phytoremediation capacity from contaminated soil.

Recently, Dr. YANG Wei and Prof. WEI Shuhe from the Institute of Applied Ecology (IAE) of Chinese Academy of Sciences determined the Cd concentration accumulated by S. nigrum, the pH and the extractable Cd concentration in soil, also evaluated the biomasses of the root and aboveground of S. nigrum and Cd phytoaccumulation capacity. Moreover, the relationship of shoot extractions, root and shoot biomasses of S. nigrum and N concentration in soil were statistically analyzed, respectively.

The results showed that S. nigrum biomass increased with the increase of N concentration up to 800 mg kg^-1, in which the biomass reached maximum and no longer improved. Furthermore, when N fertilizers (NH₄HCO₃, NH₄Cl, (NH₄)₂SO₄ and CH₄N₂O) were elevated to 800 mg kg^-1, the biomasses at the aboveground part of S. nigrum parts improved to the maximum under (NH₄)₂SO₄ and CH₄N₂O treatments, increased by 5.92- and 5.89-fold, respectively, compared to the control with no N fertilizer supply.

In addition, correlation analysis revealed that the accumulation of Cd at the aboveground parts and root and shoot biomasses of S. nigrum were significantly and positively related to the concentration gradient of N fertilizer.

These results demonstrate Cd phytoextraction efficiency and phytoremediation capacity of S. nigrum are the strongest as exposed to (NH₄)₂SO₄ and CH₄N₂O fertilizers at N concentration of 800 mg kg^-1.

This work was financially supported by the Special Plan in the Major Research & Development of the 13rd Five-Year Plan of China, the National Natural Science Foundation of China, Projects of Shaanxi Province, and the project of Foreign Experts Bureau of Shaanxi province.

The study entitled " Strengthening role and the mechanism of optimum nitrogen addition in relation to Solanum nigrum L. Cd hyperaccumulation in soil " was published in Ecotoxicology and Environmental Safety.