Periphyton has the potential to increase phosphorus use efficiency in paddy fields.

The phosphorus (P) supply is mismatched with rice demand in the early and late stages of rice growth, which primarily results in low P use efficiency and high environmental risk. In recent years, the use of the natural periphyton in nutrient regulation in paddy fields has attracted much research interest. However, a mechanistic understanding of the action of periphyton on P biogeochemical cycling during the pivotal stages of rice growth has received little attention. In this study, the influence of periphyton proliferation on the soil surface and its consequential decomposition on P migration and bioavailability were investigated in two paddy soils using two microcosm experiments. The results showed that periphyton rapidly accumulated fertilizer P when it proliferated on the soil surface under favorable light condition, which led to more fertilizer P being stored on the soil surface and less P being fixed by soil particles or transported via runoff into the water bodies. The decomposition of periphyton under unfavorable light condition not only increased soil soluble reactive P, but also increased the amount of easily available P species, such as labile P, AlP, FeP, and mobilized OP. Thus, periphyton colonizing the soil surface in the early stage of rice growth could act as a P sink and decrease the P environmental risk, and its decomposition in the late stage of rice growth could act as a P source and activator. Phosphorus bioavailability regulated by periphyton could be synchronous with rice needs. Thus, periphyton has the potential to increase P use efficiency in paddy fields.