EVALUATING PHOSPHORUS SOLUBILITY IN TUNDRA AND BOREAL ECOSYSTEMS

Northern tundra and boreal peatlands regions store some of the largest pools of organic carbon on the planet. Increases in temperature and changes in hydrologic regimes are destabilizing these soil carbon pools, accelerating the decomposition of organic matter and subsequent release of the greenhouse gases carbon dioxide (CO₂) and methane (CH₄) to the atmosphere. However, northern peatlands have the potential to act as massive carbon sinks if sufficient nutrients are available to support increased plant growth under warming climate conditions. The ability of vegetation to obtain dissolved phosphorus for enhanced growth potentially depends on the presence of iron (Fe) oxyhydroxide minerals in the soil. Phosphorus bioavailability is limited when phosphate ions bind strongly to Fe(III)-oxyhydroxides, which precipitate in soils at oxic-anoxic interfaces due to oxidation of dissolved Fe²⁺ ions. Our objective is to quantify iron oxyhydroxide concentrations and the phosphate (PO₄^3-) sorption potentials of organic and mineral soils obtained from Northern Minnesota and Alaska that have been developed across topographic and saturation gradients. Phosphate sorption potential was evaluated by reacting soils with known concentrations of dissolved phosphate and analyzing the amount of phosphate left in solution using Ultraviolet Visible Spectrophotometry (UV-Vis). Results indicate that saturated, organic-rich soils in topographic lows have higher phosphate sorption potentials than unsaturated soils in topographic highs, possibly due to a higher concentration of poorly-crystalline iron oxide minerals in these sites. Therefore, continued temperature increase in tundra and boreal regions may subsequently alter phosphorus bioavailability with sorption to poorly-crystalline iron oxides at the oxic-anoxic boundary of a progressively lowering water table.