In-situ phytoextraction of Ni by a native population of Alyssum murale on an ultramafic site (Albania)

Ultramafic outcrops are widespread in Albania and host several Ni hyperaccumulators ( e.g., Alyssum murale Waldst. & Kit.). A Weld experiment was conducted in Pojske ( Eastern Albania), a large ultramafic area in which native A. murale was cultivated. The experiment consisted in testing the phytoextraction potential of already installed natural vegetation ( including A. murale) on crop Welds with or without suitable fertilisation. The area was divided into six 36-m(2) plots, three of which were fertilised in April 2005 with ( NPK + S). The soil ( Magnesic Hypereutric Vertisol) was fully described as well as the mineralogy of horizons and the localisation of Ni bearing phases ( TEM-EDX and XRD). Ni availability was also characterised by Isotopic Exchange Kinetics (IEK). The flora was fully described on both fertilised and unfertilised plots and the plant composition ( major and trace elements) and biomass ( shoots) harvested individually were recorded. The soil had mainly two Ni-bearing phases: high-Mg smectite ( 1.3% Ni) and serpentine ( 0.7% Ni), the first one being the source of available Ni. Ni availability was extremely high according to IEK and confirmed by Ni contents in Trifolium nigriscens Viv. reaching 1,442 mg kg(-1) ( A new hyperaccumulator?). Total biomass yields were 6.3 t ha(-1) in fertilised plots and 3.2 t ha(-1) in unfertilised plots with a highly significant effect: fertilisation increased dramatically the proportion of A. murale in the plots ( 2.6 t ha(-1) vs. 0.2 t ha(-1)). Ni content in the shoots of A. murale reached 9,129 mg kg(-1) but metal concentration was not significantly affected by fertilisation. Phytoextracted Ni in total harvest reached 25 kg Ni ha(-1) on the fertilised plots. It was significantly lower in unfertilised plots ( 3 kg Ni ha(-1)). Extensive phytomining on such sites could be promising in the Albanian context by domesticating already installed natural populations with fertilisation.