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Microscale patchiness leads to intraspecific internal nutrient heterogeneity in phytoplankton

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Uploaded on Nov 23, 2011

Microscale patchiness leads to large and important intraspecific internal nutrient heterogeneity in phytoplankton:
Phytoplankton stoichiometry or nutrient content has been shown to vary in a number of dimensions (species, condition, time, space), but the heterogeneity within a species at a given time and location, and the underlying mechanisms and importance have not been explored. There are a number of mechanisms that can create intraspecific heterogeneity, and theory suggests it can affect the population growth rate. We studied heterogeneity in P content of the freshwater diatom Cyclotella meneghiniana in the Charles River in Boston. Single-cell observations using synchrotron-based x-ray fluorescence (SXRF) show that the nutrient status varies from P-starved to -replete. We simulate individual cells using an agent-based model (ABM) that accounts for a number of mechanisms that can create heterogeneity, including surface area-based uptake, mortality differentiation, stochastic biological variability in states and behavior, macroscale mixing, and microscale nutrient patch encounter. By performing a number of simulations with various mechanisms turned on/off and comparing to data, we conclude that the heterogeneity is mostly due to microscale patchiness (85%). We explore the importance of accounting for heterogeneity in models by performing a simulation with the growth rate based on the population-average internal nutrient, as is done in conventional population-level models. This shows that ignoring heterogeneity increases the population growth rate by a factor of 1.47. To account for different heterogeneity in the lab and field, population-level ecosystem models should reduce maximum growth rates. The magnitude of this correction depends on local conditions, and in our case it is a factor of 0.72.
(Vanni Bucci, Daliangelis Nunez-Milland, Benjamin S. Twining, Ferdi L. Hellweger, Aquatic Ecology, accepted)

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