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The study of the rhizospheric microbiome in native plants should be a prerequisite before carrying out the phytomanagement of mine tailings. The goal of this work was to evaluate the rhizospheric microbiome of Piptatherum miliaceum in semiarid mine tailings. A comprehensive edaphic characterization was performed including the description of soil microbial composition in the rhizosphere of P. miliaceum growing at a mine tailings pile and at a control site. Plant nutritional and isotopic compositions were also determined. Neutral pH of the tailings (7.3) determined low metal extractability in 0.01 M CaCl2 (e.g. < 1 mg/kg for Zn). In spite of the contrasting edaphic fertility conditions of both sites, N (~ 15 g kg−1) and P (~ 400 mg kg−1) leaf concentrations were similar. The lower δ15N at the tailings plants (− 4.50‰) compared to the control (6.42‰) indicated greater efficiency of P. miliaceum for uptaking N under the low fertility conditions of the tailings (0.1% total soil nitrogen). The presence at the tailings of bacterial orders related to the cycling of N, such as Rhizobiales, could have contributed to enhance N acquisition. The lower leaf δ13C values at the tailings (− 30.22‰) compared to the control (− 28.47‰) indicated lower water use efficiency of the tailing plants. Some organotrophic bacterial and fungal groups in the tailings' rhizospheres were also found in the control site (e.g. Cytophagales, Sphingobacteriales for bacteria; Hypocreales, Pleosporales for fungi). This may indicate that P. miliaceum is able to shape its own specific microbiome at the tailings independently from the initial microbial composition of the tailings. [ABSTRACT FROM AUTHOR]

Mining wastes may pose risk nearby urban and agricultural areas. We investigated a lettuce crop land close to a former capped mine tailing in order to determinate the metal uptake by crops. Soil plot sampling design within the crop area and two transects along the tailing were performed. In addition, lettuces (root and leaves) were analyzed after transplant and harvest. The results showed a pH of around 7–8 for all the soil samples. Total metal concentrations were as follows: 190–510 mg kg−1 Pb, 13–21 mg kg−1 Cu, and 210–910 mg kg−1 Zn. Diethylene triamine pentaacetic acid-extractable Pb was around 18% of the total Pb in some samples. Transects along the base and on the plateau of the tailing showed high metal concentrations of Pb (up to 5,800 mg kg−1) and Zn (up to 4,500 mg kg−1), indicating that capping layer had been eroded. Lettuce leaves showed Pb concentrations within standard for human health (<0.3 mg kg−1 in fresh weight). For essential micronutrients such as Cu and Zn, leaves had optimal content (10–28 mg kg−1 Cu, 60–85 mg kg−1 Zn). A continued monitoring in metal uptake is needed in crop lands close to mining wastes in order to prevent risks in food safety. Capped tailings must be monitored and rehabilitation works performed from time to time. [ABSTRACT FROM AUTHOR]

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 one of the main environmental problems in post-mining landscapes and their removal is often complicated due to their high heavy metal content and dimensions. In this sense, using plant species for in situ stabilization may be an interesting and low cost option. Moreover, there are some plant species that have adapted to these conditions and are usually present at these contaminated sites. In this study, a mine tailing located in South-East Spain was investigated in order to establish lines for further phytostabilization research. A plot sampling design was carried out in order to characterize the soil properties. In addition, two plant species that have naturally colonized some parts of the tailing, Hyparrhenia hirta and Zygophyllum fabago, were sampled, including the analyses of their respective rhizospheric soils. The results of plot soil samples showed pH values from ultra acid to slightly alkaline. The electrical conductivity values were around 4dSm−1 in plots with vegetation and 8dSm−1 in the plot without vegetation. Total metal concentrations were high (4000mgkg−1 for Pb, 9000–15000mgkg−1 for Zn). DTPA- and water-extractable Zn were 5% and 3% of the total, respectively. H. hirta accumulated around 150mgkg−1 Pb in both shoots and roots. Zn concentration was 750mgkg−1 in Z. fabago shoots. DTPA-extractable Zn and Cu were positively correlated to plant uptake. [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]

Phytomanagement of tailings requires the use of soil conditioners to favour plant establishment, but their benefits on soil microbial composition need to be assessed. The goal of this work was to evaluate the effect of two organic amendments, manure compost and biochar, on soil bacterial and fungal composition at metallic mine tailings. The addition of compost caused stronger effects in most of soil parameters and microbial composition than biochar, especially at the initial stage of the experiment. However, the higher dependence on labile organic carbon for some bacterial groups at the treatments containing compost determined their decay along time (Flavobacteriales , Sphingobacteriales) and the appearance of other taxa more dependent on recalcitrant organic matter (Xanthomonadales , Myxococcales). Biochar favoured bacterial decomposers (Actinomycetales) specialised in high lignin and other recalcitrant carbon compounds. Unlike bacteria, only a few fungal orders increased their relative abundances in the treatments containing compost (Sordariales and Microascales) while the rest showed a decrease or remained unaltered. The mix biochar-compost may result the best option to support a more diverse microbial population in terms of soil functionality that is able to decompose both labile and recalcitrant carbon compounds. This may favour the resilience of the system against environmental stressors. [Display omitted] • Compost increased dissolved nitrogen and organic carbon in comparison to biochar. • Shifts in bacterial orders were related to decreases in dissolved organic carbon. • Unlike bacteria, fungal composition was less impacted by compost. • Mix compost-biochar may support higher functionality of the microbial composition. [ABSTRACT FROM AUTHOR]

Phytomanagement has been considered a feasible technique to decrease the environmental risks associated to mine tailings and its implementation relies on a suitable plant species selection. The goal of this study was to identify the edaphic factors, including microbiology, affecting the establishment of plant species with contrasting growth patterns during the phytomanagement of mine tailings. For this purpose, a comprehensive rhizosphere characterization was performed in an early ruderal colonizer, Zygophyllum fabago and two late successional tree species, Pinus halepensis and Tetraclinis articulata, growing at a mine tailings pile in southeast Spain. The neutral pH of the tailings determined low 0.01 M CaCl 2 metal extractable concentrations (e.g. <10 μg kg−1 Pb and Cd). Thus, other soil properties different from metal concentrations resulted more determining to explain plant establishment. Results revealed that Z. fabago selectively colonized tailings patches characterized by high salinity (3.5 dS m−1) and high silt percentages (42%), showing a specific halotolerant rhizospheric microbial composition, such as the bacterial Sphingomonadales and Cytophagales orders and the fungal Pleosporales and Hyprocreales orders. The two tree species grew at moderate salinity areas of the tailings pile (1.7 dS m−1) with high sand percentages (85%), where Actinomycetales was the most abundant bacterial order (>10% abundance). The contrasting mycorrhizal behaviour of both tree species (ectomycorrhizal for P. halepensis and endomycorrhizal for T. articulata) could explain the differences found between their fungal rhizospheric composition. In terms of phytomanagement, the selective plant species colonization following specific soil patches at mine tailings would increase their biodiversity and resilience against environmental stressors. • Ruderal Zygophyllum fabago colonized high salinity patches at tailings. • Trees established at the lower salinity areas of the tailings. • Actinomycetales bacterial order was the most abundant at tailings rhizospheres. • Fungal composition at trees was determined by their endo/ecto mycorrhizal behaviour. [ABSTRACT FROM AUTHOR]

Urban organic waste materials may find a potential use as amendments in agricultural or environmental fields. However, before being applied in field practices, urban organic wastes must meet some environmental and legal requirements. The objective of this work was to assess the metal (Cd, Cu, Mn, Pb and Zn) extractability in two amended degraded semiarid soils (a former agricultural soil and a mine tailings soil) employing an urban organic waste amendment. A seven-steps sequential extraction procedure was performed in order to determine the changes in metal (Cd, Cu, Mn, Pb and Zn) fractionation, after two weeks and after eight months of soil incubation in pots. The urban organic waste increased organic carbon at both soils but it did not affected pH. At both soils, the addition of the amendment increased the labile fractions of metals, especially Cu (up to 13% of total content). In the amended agricultural soil the incubation favoured the fractions associated to Mn oxides (for Mn and Zn) and organic matter (for Cu), probably due to the higher buffer capacity of the soil (pH ~ 8, high CaCO 3 , loam texture). In the amended mine tailings soil, with lower buffer capacity (pH ~ 7, low CaCO 3 , loamy sand texture), there was a redistribution into more labile fractions associated to carbonates (Mn, Pb and Zn). In low buffer capacity soils, such as the case of the mine tailings soil, the changes generated by the mineralisation of the organic matter may alter heavy metal fractionation promoting the increase of carbonate bound fractions, which could be easily mobilisable. The assessment of the long-term dynamics of organic matter mineralisation and its relation to metal geochemistry is necessary to provide a safe employment of this urban organic waste for restoring degraded soils. [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]