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This study determined the changes in trace elements (TE) (As, Cd, Cu, Ni, Pb, Zn) chemistry in the soils of a willow ("Fish Creek" - Salix purpurea, SV1 - Salix x dasyclados and SX67 - Salix miyabeana) plantation growing under a cold climate during a three-year trial. The soil HNO 3 -extractable and H 2 O-soluble TE concentrations and pools significantly decreased under most cultivars (Fish, SX67). Yet, TE changes showed inconsistent patterns and localized soil TE increases (Ni, Pb) were measured. Temporal changes in soil TE were also detected in control plots and sometimes exceeded changes in planted plots. Discrepancies existed between the amount of soil TE change and the amount of TE uptake by willows, except for Cd and Zn. Phytoremediation with willows could reduce soil Cd and Zn within a decadal timeframe indicating that they can be remediated by willows in moderately contaminated soils. However, the time needed to reduce soil As, Cu, Ni and Pb was too long to be efficient. We submit that soil leaching contributed to the TE decrease in controls and the TE discrepancies, and that the plantation could have secondary effects such as the accelerated leaching of soil TE.

The phytoextraction of the trace elements (TEs) As, Cd, Cu, Ni, Pb, and Zn by willow cultivars (Fish Creek, SV1 and SX67) was measured during a 3-year field trial in a mildly contaminated soil. Biomass ranged from 2.8 to 4.4 Mg/ha/year at 30,000 plants/ha. Shoots (62%) were the main component followed by leaves (23%) and roots (15%). Biomass was positively linked to soluble soil dissolved organic carbon, K, and Mg, while TEs, not Cd and Zn, had a negative effect. The TE concentration ranking was: Zn > Cu > Cd > Ni, Pb > As, and distribution patterns were: (i) minima in shoots (As, Ni), (ii) maxima in leaves (Cd, Zn), or (iii) maxima in roots (Cu, Pb). Correlations between soil and plant TE were significant for the six TEs in roots. The amounts extracted were at a maximum for Zn, whereas Fish Creek and SV1 extracted more TE than SX67. More than 60% (91-94% for Cd and Zn) of the total TE was in the aboveground parts. Uptake increased with time because of higher biomass. Fertilization, the selection of cultivars, and the use of complementary plants are required to improve productivity and Cd and Zn uptake.

Although plants introduced for site restoration are pre-selected for specific traits (e.g. trace element bioaccumulation, rapid growth in poor soils), the in situ success of these plants likely depends on the recruitment of appropriate rhizosphere microorganisms from their new environment. We introduced three willow (Salix spp.) cultivars to a contaminated landfill, and performed soil chemical analyses, plant measurements, and Ion Torrent sequencing of rhizospheric fungal and bacterial communities at 4 and 16 months post-planting. The abundance of certain dominant fungi was linked to willow accumulation of Zn, the most abundant trace element at the site. Interestingly, total Zn accumulation was better explained by fungal community structure 4 months post-planting than 16 months post-planting, suggesting that initial microbial recruitment may be critical. In addition, when the putative ectomycorrhizal fungi Sphaerosporella brunnea and Inocybe sp. dominated the rhizosphere 4 months post-planting, Zn accumulation efficiency was negatively correlated with fungal diversity. Although field studies such as this rely on correlation, these results suggest that the soil microbiome may have the greatest impact on plant function during the early stages of growth, and that plant-fungus specificity may be essential., (© 2015 Society for Applied Microbiology and John Wiley & Sons Ltd.)

The effect of soil properties on trace element (TE) extraction by the Fish Creek willow cultivar was assessed in a 4-month greenhouse experiment with two contrasted soils and two mycorrhizal treatments (Rhizophagus irregularis and natives). Aboveground tissues represented more than 82 % of the willow biomass and were the major sink for TE. Cadmium and Zn were concentrated in leaves, while As, Cu, Ni, and Pb were mostly found in roots. Willow bioconcentration ratios were below 0.20 for As, Cu, Ni, and Pb and reached 10.0 for Cd and 1.97 for Zn. More significant differences in willow biomass, TE concentrations, and contents were recorded between soil types than between mycorrhizal treatments. A slight significant increase in Cu extraction by willow in symbiosis with Rhizophagus irregularis was observed and was linked to increased shoot biomass. Significant regression models between TE in willow and soil properties were found in leaves (As, Ni), shoots (As, Cd, Cu, Ni), and roots (As, Cu, Pb). Most of the explanation was shared between soil water-soluble TE and fertility variables, indicating that TE phytoextraction is related to soil properties. Managing interactions between TE and major nutrients in soil appeared as a key to improve TE phytoextraction by willows.

Concentrations of nine trace elements (Ba, Cd, Cr, Cu, Mn, Ni, Pb, Tl and Zn) were measured in a plant bearing allergenic pollens (ragweed) and their transfers from soils to the roots and then to the pollens were investigated. The soil, roots and pollens collected from flowers were sampled at 26 urban sites. Soil pH, soil organic carbon and total-recoverable trace elements (TE) in soil, roots and pollens were measured. The three biogeochemical compartments are well discriminated according to their TE concentrations. The concentrations (in μg g(-1)) in pollens decreased as follow: Zn (59.5-205)>Mn (19.4-117)>Ba≈Cr≈Cu≈Ni≈Pb (0.54-27.7)>Cd (0.06-0.77)>>Tl (0.0015-0.0180). Mean elemental allocation within ragweed always favored roots over pollen but, at site level, inverse pattern is also observed mostly for Zn and slightly for Cu and Ni. Significant predictive models of TE concentrations in pollens were obtained using soil or root properties only for Cd, Ni and Pb. They all involved positive relationships between TE concentrations in pollens and in soil or roots. Estimates of short-term exposure of human to TE carried out by ragweed pollens indicate TE absorption of less than 50 ng, far below thresholds of air quality criteria. Investigating the TE chemistry of pollens is a required first step to validate the impact of TE in pollens on human health and on the prevalence and intensity of allergy symptoms and atopic diseases., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The influence of microbial activity on the concentration and speciation of trace elements (TEs) was assessed in a study on the bioavailability of TEs for edible plants. A growth chamber experiment with spring wheat (Triticum aestivum cv. USU-Perigee) was conducted and the bulk (Bk) and the rhizosphere (Rz) soil components were collected at maturity. A characterization of the microbial activity and population was made by measuring the microbial biomass, enzymes (acid phosphatase, arylsulfatase, dehydrogenase and urease) and 16S rDNA DGGE profiles. In soil water extracts, major solutes (H(+), Ca, Mg, Na, NH(4), K, Cl, NO(3), SO(4), total N, DON and DOC) and trace elements (Al, As, Cd, Ce, Cr, Cu, Fe, Pb, Tl, and Zn) including monomeric Al species, free Cu(2+) and labile Zn were determined. The partition of the variation indicated that 12.1% of the distribution of TEs in the Bk soil was significantly and exclusively explained by chemical properties while this value was less than 0.1% for the Rz soil. To the contrary, microbial properties contributed significantly to 12.3% of the distribution of TEs in the Rz soil whereas it explained less than 0.1% for the Bk soil. Detailed redundancy analyses identified several potential mechanisms (e.g. weathering of primary mineral, solubilisation of sesquioxides, bacterial effect on the redox status) explaining the fate of TEs in the Bk and Rz soils. This study revealed that microbial activity is strongly associated to the speciation of trace elements in the Rz of edible plants and points to some microbial processes influencing TE speciation.

This study focuses on the relationships of dissolved Al and Zn speciation with microbial and chemical soil properties in the bulk and rhizosphere of forest soils. The soil components were sampled under Populus tremuloides Michx. at six sites located close to industrial facilities. Total water-soluble (Al(WS), Zn(WS)) and reactive (Al(R), Zn(R)) Al and Zn concentrations measured in soil water extracts, speciation data modeled by WHAM 6, chemical properties (pH, DOC, major cations and anions) and microbial properties (microbial biomass and enzyme activities) were measured on all soils. Enrichment in Al(R) and Zn(R) was observed in the rhizosphere compared to bulk soils. In a given soil material, the speciation of Al and Zn varied according to solution pH and Al-organic as well as Zn-organic complexes or Zn(2+) were generally the dominant species. The factors controlling the Al(WS), Zn(WS), Al(R) and Zn(R) concentrations differed between soil components, shifting from strictly chemical in the bulk (78%) to interactions among microbial and chemical variables in the rhizosphere (87%). Results further indicate that organic matter and pH were significantly linked to these response variables in the rhizosphere. Involvement of rhizospheric microorganisms occurred via pH changes induced by either the microbial assimilation of nitrogen or through the release of metals during the mineralization of roots. Our results therefore suggest that microbial activity is an important component of the biogeochemistry of Al and Zn in the rhizosphere. The study further provides key information to improve the assessment of ecological risk associated to Al and Zn in forest soils.

We report the solid-liquid partitioning of Cd, Cu, Ni, Pb, and Zn in 60 organic horizon samples of forest soils from the Hermine Watershed (St-Hippolyte, PQ, Canada). The mean Kd values are respectively 1132, 966, 802, 3337 and 561. Comparison of those Kd coefficients to published compilation values show that the Kd values are lower in acidic organic soil horizons relative to the overall mean Kd values compiled for mineral soils. But, once normalized to a mean pH of 4.4, the Kd values in organic soil horizons demonstrate the high sorption affinity of organic matter, which is either as good as or up to 30 times higher than mineral soil materials for sorbing trace metals. Regression analysis shows that, within our data set, pH and total metal contents are not consistent predictors of metal partitioning. Indeed, metal sorption by the solid phase must be studied in relation to complexation by dissolved organic ligands, and both processes may sometime counteract one another.