Lc. Batty et al., The effect of pH and plaque on the uptake of Cu and Mn in Phragmites australis (Cav.) Trin ex. Steudel, ANN BOTANY, 86(3), 2000, pp. 647-653
The physico-chemical properties of iron oxyhydroxide plaques formed on the
roots of Phragmites australis under field and laboratory conditions were de
termined using electron microscopy and energy dispersive spectrometry (EDS)
analysis. Plaques were present as an amorphous coating on roots with an un
even distribution. They were shown to be composed of iron in both the field
and laboratory, and phosphorus was found to be adsorbed onto the surface o
f plaques formed in the laboratory. The uptake of copper and manganese in t
he presence and absence of plaque was investigated under two different pH r
egimes. Concentrations of Cu were lower in the shoots of P. australis in th
e presence of plaque (565 mg kg(-1)) than when it was absent (1400 mg kg(-1
)), under growth conditions of higher pH (6.0). The adsorption of Cu and Mn
onto the plaque surface was not the mechanism by which plaque reduced the
uptake of other metals. Alternatively, the plaque may simply act as a physi
cal barrier. Under conditions of lower pH (3.5) the activity of hydrogen io
ns at the root surface interfered with the movement of metals into the root
and masked any potential effect of iron plaque. (C) 2000 Annals of Botany
Company.