Metal accumulation by Alyssum serpyllifolium subsp. malacitanum Rivas Goday (Brassicaceae) across different petrographic entities in South-Iberian ultramafic massifs: plant-soil relationships and prospects for phytomining

In the ultramafic area of Spain, a high quantity of petrographic entities is present. Data on the variability among populations of hyperaccumulation are scarce. We investigated Alyssum serpyllifolium subsp. malacitanum for variations in eleven elements among populations growing in different ultramafic massifs in different petrographic entities (dunites, harzburgite-pyroxenic dunite, harzburgite-lherzolite, pyroxenite, and serpentinites). Samples of leaves and soils were collected from the ultramafic outcrops of Sierra Bermeja and Sierra de Mijas (Andalusia, Spain). The concentrations of Ni, Fe, Mg, Si, Cr, Co, Sr, Mn, Cu, Zn, and Ba and the bioaccumulation factors (BAF) were determined. Although analysis of variance of the data for each element revealed considerable variation in soil chemistry (for Fe, Mg, Sr, and Ba) among the different petrographic entities, population-level variation with regard to the hyperaccumulation in the leaves was not detected. BAF values >1 were obtained for Sr and Ni depending on the petrographic entities. The correlation detected between the concentration of Ni in leaves and concentration in soil is relevant. The population-level variation obtained in the BAF values for Sr and Ni provides comprehensive information on the natural variation of hyperaccumulation. The BAF obtained for Ba is an important result for phytomining. Novelty statement To date, studies of hyperaccumulation in plant tissues on ultramafic rocks have not considered the great diversity of petrographic entities in the world's outcrops. One of them is the one that we studied in Spain with more than eight petrographic entities and different soils. Our hypothesis is that the different chemical compositions of the soils in ultramafic rocks significantly affect the hyperaccumulation of metals by specialized plants, which may have consequences for phytomining. For this purpose, individuals, populations, and different soils have been tested and the results have been subjected to the corresponding statistical tests. The obtained knowledge reflects the different behavior of the studied plant not only for the Ni: the obtained results for Sr and for Ba revealed interesting results for the hyperaccumulation in Alyssum of both metals.