MEPS 434:29-43 (2011)  -  DOI: https://doi.org/10.3354/meps09149

ABSTRACT: Size scaling of phytoplankton growth rates and size-dependent carbon to nitrogen (C:N) stoichiometry determine phytoplankton size structure and coupling of carbon and nitrogen cycling of marine ecosystems. They are critical in predicting the growth of phytoplankton spanning a wide range of sizes and their consequences for the biological pump in marine ecosystem models. The size scaling of phytoplankton growth and size-dependent C:N stoichiometry are modelled by embedding size-dependent light-harvesting, nutrient acquisition and storage into Droop’s quota-dependent phytoplankton growth model. The size-scaling exponent of maximum growth rate of phytoplankton is –0.17 (which is higher than the universal size-scaling exponent of –1⁄4 predicted by the metabolic theory of ecology) under saturated light and NO₃. The size-scaling exponent of growth rate (μ) decreases with increasing light under saturated NO₃, and decreases with decreasing NO₃ concentration under saturated light. The allometry of equilibrium cellular C and N quota varies with light and NO₃ concentrations. Under saturated light and NO₃ concentration, C:N increases slightly with cell size. Under limiting light, but saturated NO₃, C:N is close to the Redfield ratio and is not size dependent. Under limiting NO₃ but saturated light, C:N is higher than the Redfield ratio and increases with cell size. We identified the uncertainty of the size-scaling exponent of μ associated with key parameters, for which more data need to be collected in the lab and field.

KEY WORDS: Phytoplankton growth · Size scaling · Community structure · C:N · Transport network · Quota