In-situ phytoextraction of Ni by a native population of Alyssum murale on an ultramafic site (Albania)
Résumé
Ultramafic outcrops are widespread in Albania and host several Ni hyperaccumulators (e.g., Alyssum murale Waldst. & Kit.). A field 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 fields with or without suitable fertilisation. The area was divided into six 36-m2 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.