Polyphosphate plays a vital role in the phosphorus dynamics of stream periphyton

Interest in the role of polyphosphate (polyP) in marine biogeochemical cycles has been considerable, and the likelihood is high that polyP plays a critical role in the P dynamics of stream periphyton. We monitored the effects of P pulses during natural storm events in a single stream, manipulated P pulses in stream mesocosms, and sampled 23 streams at base flow across a landscape P gradient to ascertain patterns in periphyton polyP content and formation. We found that: 1) P pulses in natural storm runoff could stimulate polyP accumulation in periphyton, 2) periphyton communities were capable of using P delivered in a single pulse for future growth and biomass accumulation, and 3) polyP can accumulate relative to microbial biomass and total microbial P under P-poor conditions. PolyP formation under P-stressed conditions might represent a reallocation of resources away from growth to maximize uptake and storage of P in future pulses. Overall, polyP may serve as an important P-retention mechanism in oligotrophic stream ecosystems.