A rhizobox experiment was conducted to compare iron (Fe) oxidation and changes of pH, redox potential (Eh) and fractions of zinc (Zn) and lead (Pb) in rhizosphere and non-rhizosphere soils of four emergent-rooted wetland plants (Echinodorus macrophyllus, Eleocharis geniculata, Hydrocotyle vulgaris and Veronica serpyllifolia) with different radial oxygen loss (ROL) from roots. The results indicated that all these wetland plants decreased pH and concentration of Fe(Ⅱ) but increased the Eh in the rhizosphere soils. Pb and Zn were transformed from unstable fractions to more stable fractions in the rhizosphere soils, so decreasing their potential metal mobility factors (MF). Among the four plants, E. macrophyllus, with the highest ROL and root biomass, possessed the greatest ability in formation of Fe plaque and in the reduction of heavy metal MFs in the rhizosphere soil. Wetland plants, with higher ROLs and root biomass, may thus be effective in decreasing potential long-term heavy metal bioavailabilities.
Lead and Zn uptake and chemical changes in rhizosphere soils of four emergent-rooted wetland plants;Aneilema bracteatum,Cyperus alternifolius,Ludwigia hyssopifolia and Veronica serpyllifolia were investigated by two experiments:(1) rhizobag filled with "clean" or metal-contaminated soil for analysis of Pb and Zn in plants and rhizosphere soils;and (2) applied deoxygenated solution for analyzing their rates of radial oxygen loss (ROL).The results showed that the wetland plants with different ROL rates had significant effects on the mobility and chemical forms of Pb and Zn in rhizosphere under flooded conditions.These effects were varied with different metal elements and metal concentrations in the soils.Lead mobility in rhizosphere of the four plants both in the "clean" and contaminated soils was decreased,while Zn mobility was increased in the rhizosphere of the "clean" soil,but decreased in the contaminated soil.Among the four plants,V.serpyllifolia,with the highest ROL,formed the highest degree of Fe plaque on the root surface,immobilized more Zn in Fe plaque,and has the highest effects on the changes of Zn form (EXC-Zn) in rhizosphere under both "clean" and contaminated soil conditions.These results suggested that ROL of wetland plants could play an important role in Fe plaque formation and mobility and chemical changes of metals in rhizosphere soil under flood conditions.
