Abstract

The variability of ecophysiological traits associated with productivity (e.g., water relations, leaf structure, photosynthesis and nitrogen (N) content) and susceptibility to fungal and insect infection were investigated in five poplar clones (Populus deltoides Batr.—Lux clone; Populus nigra L.—58-861 clone and Populus × canadensis Mönch.—Luisa Avanzo, I-214 and Adige clones) during their growing season. The objective of the study was to determine their physiological responses under summer constraints (characteristic of the Mediterranean climate) and to propose clone candidates for environmental restoration activities such as phytoremediation. Relative water content, the radiometric water index and 13C isotope discrimination (Δ13C) results reflected improved water relations in Adige and Lux during summer drought. Leaf structural parameters such as leaf area, leaf mass per area, density (D) and thickness (T) indicated poorer structural adaptations to summer drought in clone 58-861. Nitrogen content and Δ13C results pointed to a stomatal component as the main limitant of photosynthesis in all clones. Adige and Lux showed enhanced photoprotection as indicated by the size and the de-epoxidation index of the xanthophyll-cycle pool, and also improved antioxidant defence displayed by higher ascorbate, reduced glutathione, total phenolics and α-tocopherol levels. Photoprotective and antioxidative responses allowed all clones to maintain a high maximum quantum yield of PSII (Fv/Fm) with the exception of Luisa Avanzo and 58-861 which experienced slight photoinhibition in late spring. The study of susceptibility to rust (Melampsora sp.) and lace bug (Monosteira unicostata Muls. and Rey) infections showed Adige and Lux to be the most tolerant. Overall, these two clones presented high adaptability to summer conditions and improved resistance to abiotic and biotic stress, thereby making them highly commendable clones for use in environmental remediation programmes.

Abstract

Phytostabilization is a promising option for the remediation of metal contaminated soils which requires the implementation of long-term monitoring programs. We here propose to incorporate the paradigm of "adaptive monitoring", which enables monitoring programs to evolve iteratively as new information emerges and research questions change, to metal phytostabilization. Posing good questions that cover the chemical, toxicological and ecological concerns associated to metal contaminated soils is critical for an efficient long-term phytostabilization monitoring program. Regarding the ecological concerns, soil microbial parameters are most valuable indicators of the effectiveness of metal phytostabilization processes in terms of recovery of soil health. We suggest to group soil microbial parameters in higher-level categories such as "ecological attributes" (vigor, organization, stability) or "ecosystem services" in order to facilitate interpretation and, most importantly, to provide long-term phytostabilization monitoring programs with the required stability through time against changes in techniques, methods, interests, etc. that will inevitably occur during the monitoring program. Finally, a Phytostabilization Monitoring Card, based on both ecological attributes and ecosystem services, for soil microbial properties is provided.

Abstract

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.

Abstract

Many contaminated sites are characterized by the presence of different metals, thus increasing the complexity of toxic responses in exposed organisms. Within toxicogenomics, transcriptomics can be approached through the use of microarrays aimed at producing a genetic fingerprint for the response of model organisms to the presence of chemicals. We studied temporal changes in the early gene expression profiles of Escherichia coli cells exposed to three metal doses of a polymetallic solution over three exposure times, through the application of cDNA microarray technology. In the absence of metals, many genes belonging to a variety of cellular functions were up- and down-regulated over time. At the lowest metal dose, an activation of metal-specific transporters (Cus and ZraP proteins) and a mobilization of glutathione transporters involved in metal sequestration and trafficking was observed over time; this metal dose resulted in the generation of ROS capable of stimulating the transcription of Mn-superoxide dismutase, the assembly of Fe-S clusters and the synthesis of cysteine. At the intermediate dose, an overexpression of ROS scavengers (AhpF, KatG, and YaaA) and heat shock proteins (ClpP, HslV, DnaK, and IbpAB) was observed. Finally, at the highest dose, E. coli cells showed a repression of genes related with DNA mutation correctors (MutY glycopeptidases).

Abstract

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.

Abstract

A field trial was carried out to assess the effectiveness of organic amendments (COW: cow slurry; POULTRY: poultry manure; PAPER: paper mill sludge mixed with poultry manure) for the aided phytostabilization of vegetated and non-vegetated sites of an abandoned Pb/Zn contaminated mine. A native ecotype of Festuca rubra L. was used for colonizing the initially non-vegetated sites. Two and six months after amendment application, soil Pb and Zn availability (CaCl2-extractability) decreased. COW and POULTRY treatments resulted in highest reduction in Pb extractability in non-vegetated sites. In vegetated sites, COW-treated plots showed the highest decrease in metal extractability at 6 months. All amendments, especially POULTRY, led to higher F. rubra biomass and vegetation cover in vegetated and initially non-vegetated sites, respectively. Two months after soil treatment, soil basal and substrate-induced respiration peaked in vegetated sites. Based on a root elongation bioassay with Lactuca sativa L., beneficial effects of soil amendments were also observed in terms of soil phytotoxicity. The problem of high variability (spatial, temporal and environmental) of vegetated and non-vegetated mine soils for an effective aided phytostabilization is discussed.

Summary

Tocopherols, present in plastids from all lineages of photosynthetic eukaryotes, have long been recognized as key constituents of photoprotective defenses. Membrane-bound tocopherols play an essential antioxidant role by quenching singlet oxygen and preventing the propagation of lipid peroxidation through their radical scavenging activity. However, experiments with tocopheroldefi cient plants have shown a surprisingly low impact of high light, and this apparently is the result of a functional overlap of tocopherol with zeaxanthin (Z). Apart from the role of zeaxanthin in the modulation of thermal dissipation (assessed via non-photochemical quenching of chlorophyll fl uorescence, NPQ), zeaxanthin molecules dissolved as free pigments in the membrane lipid phase or present at the lipid-protein interfaces may act as direct antioxidants and membrane stabilizers, having a synergistic effect with tocopherol. The existence of pools of unbound zeaxanthin is supported by numerous stress experiments that showed a much higher enhancement of the total pool of violaxanthin-antheraxanthin-zeaxanthin (VAZ) cycle pigments than that of their potential binding sites in antenna proteins. Tocopherol content is also subject to strong environmental modulation by stress factors, and the dynamics of the tocopherol and Z pools are frequently highly correlated. However, a signifi cant proportion of the leaf tocopherol pool accumulates in plastoglobules, instead of thylakoids, where its protective role is not so clearly established. From an evolutionary perspective, there seems to be a trend from a xanthophyll cycle-based photoprotection in algae to a more diversifi ed strategy in terrestrial plants.