Phytoplankton can accumulate polyphosphate (polyP) to alleviate limitation of essential nutrient phosphorus (P). Yet polyP metabolisms in aquatic systems and their roles in P biogeochemical cycle remain elusive. Previously reported polyP enrichment in low-phosphorus oligotrophic marine waters contradicts the common view of polyP as a luxury P-storage molecule. Here, we show that in a P-rich eutrophic bay of Lake Ontario, planktonic polyP is controlled by multiple mechanisms and responds strongly to seasonal variations. Plankton accumulate polyP as P storage under high-P conditions via luxury uptake and use it under acute P stress. Low phosphorus also triggers enrichment of polyP that can be preferentially recycled to attenuate P lost. We discover that picoplankton, despite their low production rates, are responsible for the dynamic polyP metabolisms. Picoplankton store and liberate polyP to support the high primary productivity of blooming algae. PolyP mechanisms enable efficient P recycling on ecosystem and even larger scales.
Bibliographical noteFunding Information:
We acknowledge Marianne Racine, Alexander Umbach, David Depew, Jacqui Milne and the technical field teams at the Environmental and Climate Change Canada for help with sample acquisition. We thank Dushara Ragavachari for assisting with sample filtrations, Stefan Markovic and Zach DiLoreto for laboratory technical support, Susan Watson (University of Waterloo) for discussion, and support from the Research Support Section at Environmental and Climate Change Canada. We thank Toshikazu Shiba (Matsumoto University, Japan) for providing polyphosphate standards. NSERC Discovery Grant to MD provides financial support for this project.
© 2019, The Author(s).