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Mine tailings are typical elements in post-mining landscapes which usually have high heavy metal contents and are affected by intensive erosion processes, above all in arid and semiarid areas. Revegetation of these sites is considered a low cost and suitable technology to effect surface stabilization. Spontaneous plant communities that colonize tailings in Southern Spain showed different behavior depending on the pH: in neutral tailings the plant communities were formed by less number of plant species than in acid tailings but they had less seasonal variations, showing a stable development. This spontaneous vegetation, that is adapted to metal toxicity and to drought, allows reducing air borne and water erosion, and may mitigate the spread of the contamination to the nearby areas. [Copyright &y& Elsevier]

Abstract: Mine tailings are a characteristic of landscapes where mineral extraction has occurred. These tailings usually contain high heavy metal concentrations and have low fertility. In arid and semiarid zones, erosion may be an additional problem. The removal of these tailings is often impractical due to their large volumes. Therefore, a need exists to develop in situ low cost technologies to effect surface stabilization. The use of vegetation can be an attractive option, since there are some native plant species that can colonize parts of these polluted sites unaided. Some edaphic factors were investigated, including heavy metal concentrations, in three mine tailings from a semiarid mining zone in Southeast Spain. High total metal concentrations were found: 5000–8000 mg/kg for lead and 7600–12300 mg/kg for zinc. Two of these mine tailings had pH values between 6 and 7, while the other was acidic, with a pH of 2.5. Metal solubility was pH dependent, with more than 10% of the total zinc soluble in the acid substrate and less than 1% in the neutral substrates. The metal concentrations (copper, lead and zinc) in shoots of native vegetation colonizing in these sites were studied. No species of hyperaccumulators were found. The highest concentrations were found in Zygophyllum fabago, with 530 mg/kg zinc, Helichrysum decumbens with 390 mg/kg lead, and Tamarix sp. with 11 mg/kg copper. An analysis of the rhizospheric soil of these plants indicated that Lygeum spartum grew in pH 3 soil and had low metal concentration in shoots (40 mg/kg zinc and 41 mg/kg lead). [Copyright &y& Elsevier]

Abstract The suitable phytomanaging of mine tailings not only requires an improvement of soil fertility but also the assessment of the biotic interactions between the selected plant species. This study aimed to evaluate the effect of an organic amendment on the response of two plant species of contrasting habit, a tree, Pinus halepensis and a grass, Piptatherum miliaceum growing on a metal(loid)-contaminated substrate collected from mine tailings. Pots containing single plant individuals or their combination, with and without organic amendment (at 10% rate), were established and grown in a greenhouse for 13 months. Plant biomass, foliar ionome, leaf δ15N and metal(loid) concentrations were measured at the end of the experiment. The amendment alleviated P deficiency in the substrate and strongly stimulated biomass production by both plant species (10-fold for pine; 90-fold for the grass), leading to more balanced N/P ratios in leaves (especially for the grass). Co-culture with the grass negatively affected pine growth, decreasing total biomass and leaf δ15N values and inducing severe N deficiency (leaf N/P ratio<10). In contrast, co-culture with pine improved the nutrient status and growth of the grass, but only under non-amended conditions. Needle metal(loid) concentrations in P. halepensis were affected by both amendment addition and co-culture with the grass. High biomass growth with low metal(loid) concentrations in P. miliaceum leaves for the amended treatment makes this grass species suitable for the phytomanagement of metal(loid) polluted tailings, since it achieves high biomass production together with low concentrations of metal(loid)s in edible/senescent parts. Highlights • Co-culture modulated plant performance in amended treatments. • Co-culture with the grass P.miliaceum negatively affected pine (P.halepensis) growth. • P.miliaceum showed higher competitive ability when co-cultured with P.halepensis. [ABSTRACT FROM AUTHOR]

Plant selection is a critical issue for the long-term success of phytomanagement projects. The presence of “microenvironments” related to salinity in mine tailings under semiarid climates make halophytes a suitable alternative for phytostabilisation. The goal of this work was to assess the criteria for plant species selection for the phytostabilisation of mining wastes in semiarid areas, focusing on the suitability of the employment of spontaneous halophyte plant species. For this purpose, a comprehensive soil below-plant and plant survey including spontaneous halophyte and non-halophyte plant species were performed in an extensive area covered by mining wastes in SE Spain. The soil samples collected below halophyte plants showed higher electrical conductivity, organic carbon and water extractable salts concentrations than the non-halophyte ones. Zygophyllum fabago and Limonium cossonianum were the most suitable species to colonize the salty micro niches at the tailings while Tamarix canariensis and Atriplex halimus showed the best soil fertility indicators under moderate electrical conductivity values. In general, the halophyte species showed lower metal(loid) concentrations in leaves or shoots than the non-halophyte ones ( e.g . Cistus monspeliensis , Dittrichia viscosa and Helichrysum decumbens ). Oppositely, the leaves of halophyte plant species, specially A. halimus and Z. fabago , showed higher accumulation of Na and Cl which may be of interest to effect the long term desalination of the tailings. The interest of employing halophytes is not only focused on metal(loid)s tolerance but also in the high potential for soil improvement (organic matter accumulation, desalination). The positive effects of combining halophyte with non-halophyte plant species may enhance the long-term sustainability of the plant community. [ABSTRACT FROM AUTHOR]

The goal of this work was to assess the selection of the most suitable combination of plant species for the phytomanagement of mine tailings, by comparing among different plant life-forms (grasses, shrubs and trees). A comparison on induced rhizosphere changes generated by four plant species (the grass Piptatherum miliaceum, the shrub Helichrysum decumbens, and the trees, Pinus halepensis and Tetraclinis articulata) and high density vegetation patches (fertility islands) at a mine tailing located at Southeast Spain and the description of their physiological status employing stable isotopes analyses were carried out. The edaphic niches for plant growth were determined by salinity, organic matter and total soil nitrogen while metal(loid)s concentrations played a minor role. Induced changes in plant rhizospheres had a significant impact in soil microbiology. While grasses and shrubs may play an important role in primary ecological succession, trees seem to be the key to the development of fertility islands. The low δ15N values (−8.00‰) in P. halepensis needles may reflect higher ectomycorrhizal dependence. Large differences in leaf δ18O among the plant species indicated contrasting and complementary water acquisition strategies. Leaf δ13C values (−27.6‰) suggested that T. articulata had higher water use efficiency than the rest of species (−29.9‰). The implement of a diverse set of plant species with contrasting life forms for revegetating tailings may result in a more efficient employment of water resources and a higher biodiversity not only in relation to flora but soil microbiology too. [Copyright &y& Elsevier]

Highlights: [•] CaCl2-extractable Cu was correlated with dissolved organic carbon. [•] CaCl2-extractable concentrations did not correlate with metal uptake. [•] Pinus halepensis may be used to phytostabilise metal polluted soils in semiarid areas. [•] Areas surrounding tailings were impacted by high metal(loid) concentrations. [Copyright &y& Elsevier]