High potential for iron reduction in upland soils

Changes in the redox state of iron (Fe) can be coupled to the biogeochemical cycling of carbon (C), nitrogen, and phosphorus, and thus regulate soil C, ecosystem nutrient availability, and greenhouse gas production. However, its importance broadly in non-flooded upland terrestrial ecosystems is unknown. We measured Fe reduction in soil samples from an annual grassland, a drained peatland, and a humid tropical forest. We incubated soil slurries in an anoxic glovebox for 5.5 days and added sodium acetate daily at rates up to 0.4 mg C·(g soil)^-1·d^-1· Soil moisture, poorly crystalline Fe oxide concentrations, and Fe(II) concentrations differed among study sites in the following order: annual grassland < drained peatland < tropical forest (P < 0.001 for all characteristics). All of the soil samples demonstrated high Fe reduction potential with maximum rates over the course of the incubation averaging 1706 ± 66, 2016 ± 12, and 2973 ± 115 μg Fe·(g soil)^-1·d^-1(mean ± SE) for the tropical forest, annual grassland, and drained peatland, respectively. Our results suggest that upland soils from diverse ecosystems have the potential to exhibit high short-term rates of Fe reduction that may play an important role in driving soil biogeochemical processes during periods of anaerobiosis.