Oihana Barrutia

Interactions between plant and rhizosphere microbial communities in a metalliferous soil.

In the present work, the relationships between plant consortia, consisting of 1-4 metallicolous pseudometallophytes with different metal-tolerance strategies (Thlaspi caerulescens: hyperaccumulator; Jasione montana: accumulator; Rumex acetosa: indicator; Festuca rubra: excluder), and their rhizosphere microbial communities were studied in a mine soil polluted with high levels of Cd, Pb and Zn. Physiological response and phytoremediation potential of the studied pseudometallophytes were also investigated. The studied metallicolous populations are tolerant to metal pollution and offer potential for the development of phytoextraction and phytostabilization technologies. T. caerulescens appears very tolerant to metal stress and most suitable for metal phytoextraction; the other three species enhance soil functionality. Soil microbial properties had a stronger effect on plant biomass rather than the other way around (35.2% versus 14.9%). An ecological understanding of how contaminants, ecosystem functions and biological communities interact in the long-term is needed for proper management of these fragile metalliferous ecosystems.

Native Plant Communities in an Abandoned Pb-Zn Mining Area of Northern Spain: Implications for Phytoremediation and Germplasm Preservation

Plants growing on metalliferous soils from abandoned mines are unique because of their ability to cope with high metal levels in soil. In this study, we characterized plants and soils from an abandoned Pb-Zn mine in the Basque Country (northern Spain). Soil in this area proved to be deficient in major macronutrients and to contain toxic levels of Cd, Pb, and Zn. Spontaneously growing native plants (belonging to 31 species, 28 genera, and 15 families) were botanically identified. Plant shoots and rhizosphere soil were sampled at several sites in the mine, and analyzed for Pb, Zn and Cd concentration. Zinc showed the highest concentrations in shoots, followed by Pb and Cd. Highest Zn concentrations in shoots were found in the Zn-Cd hyperaccumulator Thlaspi caerulescens (mean = 18,254 mg Zn kg−1 DW). Different metal tolerance and accumulation patterns were observed among the studied plant species, thus offering a wide germplasm assortment for the suitable selection of phytoremediation technologies. This study highlights the importance of preserving metalliferous environments as they shelter a unique and highly valuable metallicolous biodiversity.

Phytoextraction potential of two Rumex acetosa L. accessions collected from metalliferous and non-metalliferous sites: effect of fertilization.

Metal tolerance and phytoextraction potential of two common sorrel (Rumex acetosa L.) accessions, collected from a Pb/Zn contaminated site (CS, Lanestosa) and an uncontaminated site (UCS, Larrauri), were studied in fertilized and non-fertilized pots prepared by combining soil samples from both sites in different proportions (i.e., 0%, 33%, 66% and 100% of Lanestosa contaminated soil). The original metalliferous mine soil contained 20480, 4950 and 14 mg kg(-1) of Zn, Pb and Cd, respectively. The microcosm experiment was carried out for two months under greenhouse controlled conditions. It was found that fertilization increased mean plant biomass of both accessions as well as their tolerance. However, only the CS accession survived all treatments even though its biomass decreased proportionally according to the percentage of contaminated mine soil present in the pots. This metallicolous accession would be useful for the revegetation and phytostabilization of mine soils. Due to its high concentration and bioavailability in the contaminated soil, the highest values of metal phytoextracted corresponded to Zn. The CS accession was capable of efficiently phytoextracting metal from the 100% mine soil, indeed reaching very promising phytoextraction rates in the fertilized pots (6.8 mg plant(-1) month(-1)), similar to the ones obtained with hyperaccumulator plants. It was concluded that fertilization is certainly worth being considered for phytoextraction and revegetation with native plants from metalliferous soils.

Plant tolerance to diesel minimizes its impact on soil microbial characteristics during rhizoremediation of diesel-contaminated soils

Soil contamination due to petroleum-derived products is an important environmental problem. We assessed the impacts of diesel oil on plants (Trifolium repens and Lolium perenne) and soil microbial community characteristics within the context of the rhizoremediation of contaminated soils. For this purpose, a diesel fuel spill on a grassland soil was simulated under pot conditions at a dose of 12,000 mg diesel kg(-1) DW soil. Thirty days after diesel addition, T. repens (white clover) and L. perenne (perennial ryegrass) were sown in the pots and grown under greenhouse conditions (temperature 25/18 °C day/night, relative humidity 60/80% day/night and a photosynthetic photon flux density of 400 μmol photon m(-2) s(-1)) for 5 months. A parallel set of unplanted pots was also included. Concentrations of n-alkanes in soil were determined as an indicator of diesel degradation. Seedling germination, plant growth, maximal photochemical efficiency of photosystem II (F(v)/F(m)), pigment composition and lipophylic antioxidant content were determined to assess the impacts of diesel on the studied plants. Soil microbial community characteristics, such as enzyme and community-level physiological profiles, were also determined and used to calculate the soil quality index (SQI). The presence of plants had a stimulatory effect on soil microbial activity. L. perenne was far more tolerant to diesel contamination than T. repens. Diesel contamination affected soil microbial characteristics, although its impact was less pronounced in the rhizosphere of L. perenne. Rhizoremediation with T. repens and L. perenne resulted in a similar reduction of total n-alkanes concentration. However, values of the soil microbial parameters and the SQI showed that the more tolerant species (L. perenne) was able to better maintain its rhizosphere characteristics when growing in diesel-contaminated soil, suggesting a better soil health. We concluded that plant tolerance is of crucial importance for the recovery of soil health during rhizoremediation of contaminated soils.

Differences in EDTA-assisted metal phytoextraction between metallicolous and non-metallicolous accessions of Rumex acetosa L.

Two common sorrel (Rumex acetosa) accessions, one from a Zn-Pb contaminated site (CS accession) and the other from an uncontaminated site (UCS accession), were hydroponically exposed to a mixture of heavy metals (Pb(2+) + Zn(2+) + Cd(2+)) with and without EDTA at an equimolar rate. The metallicolous CS accession showed a higher tolerance to metal treatment in the absence of the chelating agent, whereas the UCS accession was especially tolerant to EDTA treatment alone. Combination of metal and EDTA treatment resulted in a higher Pb accumulation in shoots of both accessions although plants hardly showed phytotoxic symptoms. Cd and Zn uptake was not augmented by EDTA addition to the polymetallic medium. Chelant-assisted Pb accumulation was 70% higher in the CS accession than in the UCS accession, despite the fact that the former accession evapotranspired less water than the UCS accession. These results support the existence of a non-selective apoplastic transport of metal chelates by R. acetosa roots, not related to transpiration stream.

Chemical Stabilization of Metal-Contaminated Mine Soil: Early Short-Term Soil-Amendment Interactions and Their Effects on Biological and Chemical Parameters

Chemical stabilization is a cost-effective, environmentally friendly, in situ remediation technology based on the application of organic and/or inorganic amendments to reduce soil metal bioavailability. Our objective was to assess the early short-term effects of organic amendments (sheep manure—SHEEP, poultry litter—POULTRY, cow slurry—COW, paper mill sludge mixed with poultry litter—PAPER), in sterilized and non-sterilized form, on the microbial and chemical properties, as well as on the phytotoxicity, of a Cd, Pb and Zn contaminated soil. Our results provide useful information regarding (1) the effectiveness of amendments for chemical stabilization of mine soil and (2) the impact of microbial populations present in the amendments on soil native microbial communities. Microbial populations present in the amendments did not substantially modify soil microbial functional diversity, as reflected by Biolog EcoPlates™ data, except for PAPER-amended soils. We observed a good correlation between lettuce root elongation (phytotoxicity bioassay) and Cd, Pb, and Zn CaCl2-extractable concentrations in soil. SHEEP and PAPER amendments were particularly effective at increasing soil pH and reducing metal bioavailability and phytotoxicity, while POULTRY and COW led to higher values of soil microbial properties (respiration and functional diversity). Beneficial effects observed under POULTRY at the beginning of the experiment, due to the presence of easily degradable organic matter, were partially lost over time. Our results emphasize the importance of the early monitoring of soil properties (microbial and chemical) and phytotoxicity to properly identify bottlenecks during amendment selection for chemical stabilization, in terms of reduction in metal bioavailability and improvement in soil health.

Diagnosing the Impact of Traffic on Roadside Soils Through Chemometric Analysis on the Concentrations of More Than 60 Metals Measured by ICP/MS

This study aims to establish the impact of traffic pollution at two parallel roads in the province of Biscay (North of Spain). Soil samples digestions were carried out following the EPA 3051A method and the extracts were analyzed by ICP/MS. A rapid screening method for the determination of more than 60 metals is proposed. The subsequent chemometric treatment of the obtained data shows the presence of more than ten traffic related metals: Cd, Cr, Cu, Hf, Mo, Nb, Ni, Pb, Sb, Sn, Sr, Zn and Zr. Different soil types (in the old road and in the highway) can be distinguished by means of its rare earth and alkaline metal concentration. Very high concentrations of Zn were found in soil under the guard rail.

Opening Pandora's box: cause and impact of errors on plant pigment studies

Supporting from BFU 2010-15021, UPV/EHU-GV IT-624-13 grant, JAEDoc-2011-046 fellow from the Spanish National Research Council (CSIC) received by RE and Marie Curie IEF grant (328370 MELISSA) from the European FP7-PEOPLE received by BF-M, are also acknowledged.

Agro-industrial wastes as effective amendments for ecotoxicity reduction and soil health improvement in aided phytostabilization

Aided phytostabilization is a technology that uses metal tolerant plants and organic and/or inorganic amendments to reduce soil metal bioavailability, while improving soil health. Our objective was to determine the effects of the application of amendments [sheep manure (SHEEP), poultry litter (POULTRY), cow slurry (COW), and paper mill sludge mixed with poultry litter (PAPER)], together with the growth of a metallicolous Festuca rubra L. population, on (i) chemical and microbial indicators of soil health and (ii) soil ecotoxicity, during the aided phytostabilization of a Zn/Pb contaminated mine soil. Amendment application led to an increase in soil pH, organic matter content, and inorganic salts, resulting in a decrease in Pb and Zn CaCl2-extractable concentrations in soil, which, in turn, contributed to lower ecotoxicity and a stimulation of plant growth and soil microbial communities. The factor most affecting the metal extractability was probably soil pH. POULTRY was the best amendment in terms of increasing plant growth, chlorophylls content, and soil microbial biomass and activity, but resulted in higher levels of phytoavailable Pb and Zn. SHEEP and PAPER were more effective at reducing metal CaCl2-extractability and, consequently, led to lower values of metal accumulation in plant tissues, thereby reducing the risk of metals entering into the food chain. When combined with the application of organic amendments, the metallicolous F. rubra population studied here appears an excellent candidate for aided phytostabilization. Our results indicate that the application of organic amendments is essential for the short-term recovery of highly contaminated metalliferous soils during aided phytostabilization.