In this study, we test the applicability of the Droop/Caperon internal stores model to describe the growth and decline of the globally abundant marine cyanobacterium Prochlorococcus in batch culture as a function of internal and external inorganic and organic carbon and nitrogen. A rigorous parameter fitting exercise, constrained by the measured cell density, ammonium and inorganic carbon concentrations, revealed many different combinations of parameter values that provided equally good model-data fit. Introducing data on C : N ratio from the published literature provided additional constraints which could only be satisfied with a structural change to the model. The simplest addition that satisfied these constraints and improved quantitative overall model-data agreement was to explicitly represent excretion, which was predicted to account for 0.03–8.5% of the daily primary productivity; somewhat lower than previous estimates based on radiotracer incorporation. We argue that this significant and biologically meaningful process should not be neglected in models of marine phytoplankton.
Bibliographical noteFunding Information:
We thank Dr. Anne-Willem Omta, Dr. Stephanie Dutkiewicz, Dr. Oliver Jahn, Dr. George Bezerra and Drew Levin for assistance and fruitful discussions and Noga Yoselevich for graphic work. This study was supported by grant number 2010183 from the United States-Israel Binational Science Foundation (to MJF and DS) and by grant Microbes-2-Model from the European Union FP7 Marie Curie Reintegration program (to DS), and Gordon and Betty Moore Foundation Marine Microbiology Initiative #3778 and Simons Foundation (SCOPE; Simons Collaboration on Ocean Processes and Ecology) (to MJF).
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ASJC Scopus subject areas
- Aquatic Science