The Effect of pH and Plaque on the Uptake of Cu and Mn in Phragmites australis(Cav.) Trin ex. Steudel

The physico-chemical properties of iron oxyhydroxide plaquesformed on the roots of Phragmites australis under field andlaboratory conditions were determined using electron microscopyand energy dispersive spectrometry (EDS) analysis. Plaques werepresent as an amorphous coating on roots with an uneven distribution.They were shown to be composed of iron in both the field andlaboratory, and phosphorus was found to be adsorbed onto thesurface of plaques formed in the laboratory. The uptake of copperand manganese in the presence and absence of plaque was investigatedunder two different pH regimes. Concentrations of Cu were lowerin the shoots of P. australis in the presence of plaque (565mg kg^-1) than when it was absent (1400 mg kg^-1), under growthconditions of higher pH (6.0). The adsorption of Cu and Mn ontothe plaque surface was not the mechanism by which plaque reducedthe uptake of other metals. Alternatively, the plaque may simplyact as a physical barrier. Under conditions of lower pH (3.5)the activity of hydrogen ions at the root surface interferedwith the movement of metals into the root and masked any potentialeffect of iron plaque. Copyright 2000 Annals of Botany Company Phragmites australis, iron oxyhydroxide plaque, pH, manganese, copper, EDS, SEM, wetlands