Keynote lecture: Biogeochemistry of iron and interacting metals in soils

Iron is the 4th most abundant element in the Earth’s crust and in soils; its bioavailability is often limited, however, because the Fe(III) oxides and hydroxides forming at oxic, non-acidic conditions are characterized by a very low solubility. Due to their nanoparticulate size and surface properties, the vividly colored soil Fe oxides and oxihydroxides strongly sorb oxyanions as well as metal cations, hence also limit the bioavailability of other nutrients, micronutrients and toxic metals.
In contrast, microbial reduction of Fe(III) to Fe(II) drastically increases Fe solubility and bioavailability, and may release associated nutrients and toxic metals. The Fe-mediated electron cycles are often driving the redox cycles of other redox-sensitive metals, among them micronutrients and toxic metals like Se and U.
Processes like seasonal fluctuations of ground water levels, enhanced O2 diffusion along soil macropores, rhizosphere biochemistry or mineral surface-catalyzed redox processes may produce redox fronts at various spatial and temporal scales, which in turn produce complex spatial and temporal patterns of nutrient and toxin bioavailabilities.