Nickel accumulation by Alyssum serpyllifolium subsp lusitanicum (Brassicaceae) from serpentine soils of Braganca and Morais (Portugal) ultramafic massifs: plant-soil relationships and prospects for phytomining

The aim of the present study was to evaluate the possibility of using Alyssum serpyllifolium Desf. susbp. lusitanicum T.R.Dudley & P.Silva (Brassicaceae) for phytomining nickel (Ni)-rich bio-ore from serpentine soils. This species is endemic to serpentine soils of the Braganca and Morais massifs and is a Ni hyperaccumulator, containing more than 7000mgkg(-1) (dry weight) of this element. The variability of the Ni concentrations contained in the plant at different locations was verified as was its relationship with the total Ni contained in the soil or with the bioavailable Ni fraction extracted with ammonium acetate. We evaluated the biomass produced under natural conditions, and, on the basis of these values, we estimated the amount of Ni that can be removed per unit area. The results showed that considering only the aerial parts of the plant, the biomass varies between 7.04 and 9.37tha(-1), containing a range of 0.12-0.70% Ni, allowing a withdrawal of between 12.2 and 44.0kg Ni ha(-1) per crop under natural conditions.