Labile zinc concentration and free copper ion activity in the rhizosphere of forest soils

Abstract

Water-soluble and acid-extractable Cu and Zn, water-soluble organic carbon (WSOC), pH, differential pulse anodic stripping voltammetry-labile Zn (ZnL), Zn2+ activity (Windemere humic aqueous model [WHAM]; http://chess.ensmp.fr/ chemsites.html), and Cu2+ activity with an ion-selective electrode were compared between the rhizosphere and the bulk components of nine acidic forest sites from southeastern Canada. At all sites, the WSOC contents were higher in the rhizosphere than in the bulk component. Acidity was also higher in the rhizosphere, although pH differences were significant at only five sites. The concentrations of Zn in water extracts and ZnL contents (at six sites) were higher in the rhizosphere, whereas acid-extractable Zn was only marginally increased in the rhizosphere. Calculations with WHAM indicated that free Zn2+ ion activities were higher in the rhizosphere than in the bulk soil but that the fraction of total dissolved Zn in water extracts that is present as free Zn2+ did not differ significantly between the two components. The concentration of Cu in the water extract was higher in the rhizosphere for all sites, but acid-extractable Cu levels did not differ. The fraction of water-soluble Cu present as Cu2+ was higher in the bulk soil, although Cu2+ activities did not significantly vary with proximity to roots. These results showed that the processes acting in the rhizosphere of forest soils strongly affected the concentrations of dissolved Zn and Cu and that this microenvironment should be considered when estimating the bioavailability and the ecological risks of metals in soils.

Copper availability and selective microbiological properties of an intensively cultivated ultisol in Nuwara Eliya

“…In the studied cultivated soils, pH and organic C appeared as the governing factors of the populations of Cu-resistant bacteria. These chemical properties are known to influence the fluxes of various fractions of Cu 3,7,10 Correlations were also observed between the percentage of Cu-resistant bacteria and SIR (R =0.48, p<0.05) and organic C (R =0.49, p<0.05). It is known that the available C pool supports the survival of bacteria under metal stressful conditions 32 .…”

“…The fraction of Cu in soil solution is governed directly by the quality and the quantity of organic matter, clay type, amount of Fe and Al oxides in soil and indirectly by soil pH 3,5,8,9 . Copper speciation thus varied among soils with different soil characteristics 6,10 .…”

Fractionation and Speciation of Trace Elements in Soil Solution

“…As a result, a series of new interesting perspectives on ISEs application in environmental analysis has been identified [82]. For research concerning trace elements in soils, ion-selective electrodes are currently mainly used to measure free metal ion (mainly Cu 2þ ) activities for the assessment of the complexation of trace elements by organic matter [83][84][85][86], their sorption by clays [87], their mobility, availability and toxicity in soils [88][89][90] and their chemical behaviour in rhizosphere microenvironments [91]. They are also frequently used in procedures for validation of speciation models [92].…”

“…The importance of this interference depends not only on the abundance of these complexes and their contribution to the measured current, but also on their lability. Taking this uncertainty into account, ASV measurements are often operationally-defined as 'ASV-labile metal concentrations' [91].…”

Determination of Cu (II) ions using sodium salt of 4-phenylsemicarbazone 1,2-naphthoquinone-4-sulfonic acid in natural and industrial environments

“…Cu constitutes an essential micronutrient for plants (photosynthetic electron transport, metabolism of carbohydrates) and animals (pigmentation, nucleic acid, protein metabolism, integrity of immune system) (Courchesne et al 2006). Concomitantly, copper belongs to the trace elements necessary for human life.…”