Nickel uptake, partitioning, and recovery in three plant species grown in an enriched urban soil.

We investigated nickel (Ni) uptake, its partitioning, and recovery in three plant species (Alyssum argenteum All., Artemisia vulgaris L., and Dactylis glomerata L.) grown in an urban soil matrix and its Ni–enriched variant, with the aim of comparing their possible phytoextraction and/or phytostabilization behavior. The biomass was then subjected to an extraction procedure to recover Ni. A. argenteum showed strong Ni hyperaccumulation, with foliar concentrations >1000 mg/kg (dry weight) and translocation factors > 1, while D. glomerata exhibited significant root Ni uptake, with limited translocation; moreover, the specimens showed visible chlorosis and developed significantly less biomass compared to the control. A. vulgaris showed instead poor resilience and low Ni accumulation. A Principal Component Analysis revealed that the Ni–enriched soil is correlated to higher Ammonium (N–NH4+), Nitrite (N–NO2– ) and Sulfate (SO42–) soil concentrations and an increased transition metals uptake from plants; Control and Urban soils instead clustered with a higher organic matter and moisture content coupled to a different nutrient profile. Nickel enrichment increased ionic strength, sulfate concentrations and altered nutrient availability, while the high mobile Ni fraction observed initially decreased over time, suggesting a progressive fixation phenomenon occurring within the soil matrix. Elemental uptake patterns uncovered a competition between Ni and other cations, in particular, a reduced uptake of several divalent elements and the increased accumulation of selected micronutrients under stress conditions were observed. Finally, Ni was recovered from plant biomass through hydrometallurgical extraction followed by gravimetric separation.