Ferrous and other reducing forms of metals or metalloids become phytotoxic due to their increasing solubility in waterlogged soils. The roots of many wetland plant species are able to release oxygen and / or oxidants into the rhizosphere, resulting in the oxidation of ferrous to ferric iron and the precipitation of iron oxide or hydroxides on the root surface in the form of a plaque. The nature of plaque formation could reflect the biochemical conditions in the rhizosphere, which may be a function of wetla...