Departamento de Edafoloxía e Química Agrícola, Facultade de Bioloxía, Universidade de Santiago de Compostela, 15782. edcarmel@lugo.usc.es.

Abstract. The efficiency of Alyssum serpyllifolium ssp. lusitanicum (Brassicaceae), a Ni-hyperaccumulator that grows in the Tras-os-Montes region of NE Portugal on serpentine soil, for use in phytoextraction of polymetallic contaminated soils was evaluated. Here we assess changes in the bioavailability of Co, Cr, Cu, Mn, Ni, Pb and Zn, and the ability of A. serpyllifolium to access different soil metal pools. Alyssum serpyllifolium was grown on two mine-spoil soils (MS1 and MS2). The MS1 soil is contaminated with Cr (283 µg g-1) and has slightly elevated background concentrations (25-100 µg g-1) of the metals Ni, Zn and Pb, while the MS2 soil is moderately contaminated with Cr (263 µg g-1), Cu (264 µg g-1), Pb (1433 µg g-1) and Zn (377 µg g-1). Mine-soils were limed to about pHH2O 6.0 with calcium carbonate (MS1/Ca and MS2/Ca) or limed and amended with NPK fertilisers (MS1/NPK and MS2/NPK). Mine-soils that were not amended were lethal to A. serpyllifolium, plants died within 2-3 days. Biomass was reduced on MS2/Ca due to phytotoxic effects of Cu, and plants did not grow on MS2/NPK soil. In contrast, amendment with NPK fertilisers increased plant biomass by about 10-fold on MS1/NPK. However, in the same soil root dry weight was reduced by about 7-fold compared with MS1/Ca. Alyssum serpyllifolium accumulated Mn, Ni and Zn in its aerial parts (shoot[metal]/root[metal] > 1) and both metal content and transportation were generally greater in MS2 than MS1. However, metal yields were significantly increased in plants grown on MS1/NPK, due to the increment in biomass. After plant growth, concentrations of EDTA-, NH4Cl-and Mehlich 3 (M3)-extractable metals were generally lower. However, concentrations of extractable Mn and Zn were frequently greater after growth. Concentrations of M3-extractable Cr, Ni, Pb and Zn were often significantly increased in rhizosphere soils. In addition, sequential (BCR) extractions suggested that A. serpyllifolium could potentially mobilise metals from soil pools normally considered to be non plant-available, and provided that these metals are then absorbed by the plant this would increase total metal extraction. These results suggest that A. serpyllifolium could be suitable for phytoextraction uses in polymetallic-contaminated soils, and especially where the contaminants are Mn, Ni and Zn. However, its small biomass production, even on NPK fertilised mine-spoil soils, continues to be a major limiting factor for its use in phytoextraction.

Keywords: Alyssum serpyllifolium, metal bioavailability, mine-soils, phytoextraction, sequential extractions.