Cycling of reduced phosphorus compounds in soil and potential impacts of climate change

Soil phosphorus (P) remains an ever-increasing topic of importance, notably for its key role as a nutrient for driving food production but with parallel concerns for damaging water quality, all against a backdrop of uncertainty of long-term rock phosphate supplies. Soil is a key interface that holds P and regulates its onward flows to plants or leakage to waters. Often overlooked are a ubiquitous group of P compounds that exist in alternative oxidation states to that of phosphate (+5). Redox cycling, and the behavior that chemically reduced P compounds exhibit in soils, introduces alternative routes of cycling P that may become more important as the soil system itself alters, especially from the external pressures of climate change, bringing about critical dynamics in rainfall and runoff and wetting and drying. All of these factors are known to affect soil redox potential and consequently the oxidation state of soil P. This review considers the chemically reduced species in the P cycle, exploring their sources and sinks, while considering their importance within the primary global biogeochemical cycling of P and how this may be impacted by climate change in the temperate climate of the northern hemisphere.