Phytoextraction of Nickel and Cobalt by Hyperaccumulator Alyssum Species Grown on Nickel-Contaminated Soils

Several Alyssum species native to Mediterranean serpentine soils hyperaccumulate nickel. These species can potentially be used to remediate Ni-contaminated soils. However, the ability of these species to phytoextract Ni from nonserpentine Ni-contaminated soils is unknown. Two Ni hyperaccumulator species, Alyssum murale and Alyssum corsicum, were grown for 120 days on two nonserpentine Ni-contaminated soils in a greenhouse experiment. Soils were amended to provide a range of values for three soil factors: soil pH, available phosphorus, and exchangeable Ca/Mg ratio. Both species hyperaccumulated Ni, but not Co, from both soils. Ni uptake was reduced at lower soil pH and increased at higher soil pH. Neither P fertilization nor adjustment of the exchangeable Ca/Mg ratio significantly affected phytoextraction of Ni or Co. There was no difference between the two species in the amount of Ni phytoextracted, but A. corsicum phytoextracted more Co than A. murale. Higher amounts of both metals were phytoextracted from the loam than from the organic soil. Further research is needed to better understand the unusual effect of soil pH adjustment on Ni uptake by these hyperaccumulator species.