Influence of iron (oxyhydr)oxide crystallinity on phosphate bioavailability in contrasting redox and hydrological conditions

First Author's Department


Second Author's Department


Third Author's Department

Biological Sciences

Fourth Author's Department

Biological Sciences



Document Type



Hydrological shifts can change redox regimes in soils and can form poorly crystalline iron (Fe) oxides that have the potential to adsorb the limiting nutrient phosphate. The crystallinity and mineralogy of the Fe oxides that form as a function of redox fluctuations remain unknown. Phosphate bioavailability may decrease as hydrological changes drive the precipitation of Fe oxides, potentially limiting plant growth. To investigate these complex interactions, an in situ incubation experiment was conducted. Mesh bags filled with Fe-oxides of different crystallinity (ferrihydrite, goethite and hematite) were buried in and around a vernal pond in northeast Ohio. Fe-oxides were either phosphate-free or had high concentrations of sorbed phosphate. Lowland soils in vernal ponds were flooded during spring months but progressively dried out over the summer, while upland soils remained unsaturated, providing us with contrasting redox conditions. Bags were removed at two times intervals to capture flooded and dried conditions in the lowland soils. Redox conditions in the lowland soils shifted from anoxic to oxic as the pond above dried out. Fe-oxide crystallinity, analyzed using x-ray absorption fine structure spectroscopy, decreased over time for oxides incubated in the pond. Phosphate loss from phosphate-added treatments generally followed trends in Fe loss, indicating phosphate was released from dissolving iron oxides. Phosphate-free treatments in the lowlands gained phosphate over time despite losing Fe-oxides, indicating enhanced ability of small amounts of freshly precipitated Fe-oxides to adsorb phosphate. Results from this study will provide insight into the effect of Fe-oxide crystallinity on phosphate bioavailability.