Facultative Metallophyte Research Articles

Biogenic Pt uptake and nanoparticle formation in Medicago sativa and Brassica juncea

The ability of the facultative metallophyte plants, Medicago sativa (M. sativa) and Brassica juncea (B. juncea) to accumulate and translocate platinum (Pt) from aqueous substrates is reported. The influence of Pt concentration in the substrate (5, 10, 20, 40 and 80 ppm), exposure time (24, 48 and 72 h) and substrate pH (2, 3, 5, 7 and 9) was determined. In both plants the concentration of Pt increased with substrate concentration and exposure time. Greater accumulation was detected in the roots of M. sativa than B. juncea, up to a maximum of 94.19 mg Pt g−1 (dry biomass) compared with 38.5 mg Pt g−1 (dry biomass) following exposure to 80 ppm Pt after 72 h exposure, respectively. However, at lower substrate concentrations (5 and 20 ppm) greater quantities of Pt were detected in the shoots of B. juncea, ranging between 0.02 and 0.32 mg Pt g−1 (dry biomass) at 5 ppm across the different time intervals studied, compared with 0.02−0.14 mg Pt g−1 (dry biomass) for M. sativa, suggesting B. juncea to be a better translocator of Pt under idealised conditions at low concentrations. Higher Pt uptake was also observed in acidic media, with a maximum at pH 2 for M. sativa and pH 3 for B. juncea, indicating the role of net surface charge on the bioaccumulation of Pt. Once sequestered Pt(II) was reduced to Pt(0) due to the action of local metabolites. TEM images of M. sativa root samples showed the in vivo formation of Pt nanoparticles between 3 and 100 nm in size and of varying morphologies in the epidermal root cells. In vivo Pt distribution profiles were assessed using proton induced X-ray emission (μ-PIXE) spectroscopy, which showed even distribution across all tissue systems (epidermal, cortical and vascular) within the roots of both M. sativa and B. juncea.

Plant communities on metalliferous soils in northern Greece

We studied dry stony habitats with metalliferous soils (with various amounts of Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn) at low to moderate altitudes in 22 localities in northern Greece using 193 original phytosociological releves with vascular species composition, species abundance and topographical data. Soil samples were collected in 86 plots and analysed for acidity, heavy metal content and other parameters. The aims of the study were to classify the releves, describe the plant communities, assign species and communities to syntaxa, relate environment, distribution and species composition, and to compare the relative importance of soil metal content and the other environmental variables for species composition. We found 16 vegetation clusters and assigned them to 12 associations and corresponding plant communities. Each community is defi ned with respect to species composition and richness, ecology and distribution. The range of communities is heterogeneous and comprises 8 vegetation alliances belonging to the orders Alysso alyssoidis-Sedetalia, Astragalo-Potentilletalia, Hyparrhenio-Brachypodietalia ramosi, Sedo -Scleranthetalia, Thero-Brometalia and Tuberarietalia guttati. Two alliances and fi ve associations are described as new syntaxa, and several more syntaxa, including some orders, have not been recorded from Greece and the southern Balkans before. Soil acidity and, secondly, the degree of substrate consolidation and vegetation development were identifi ed as most important environmental factors explaining the chief fl oristic gradients in the data set. Heavy metal content turned out to be of secondary explanatory value, relevant in partial data sets of acidic base-poor soils or calcareous/ultramafi c soils. Most species found on metalliferous soils are therefore facultative metallophytes, while obligate metallophytes are few and characteristic of ophiolithic substrates (serpentinophytes).