NUTRIENT UPTAKE KINETICS IN PHYTOPLANKTON: A BASIS FOR NICHE SEPARATION1

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Abstract
SUMMARY: Daily patterns of incorporation of carbon dioxide and inorganic phosphate were measured in phytoplankton from Lake George, New York, in January and February 1972. Rates of photosynthesis oscillated in phase for the entire assemblage and for individual cells of the diatoms Asterionella, Tabellaria, and Fragilaria. The photosynthetic capacity was maximal in the early afternoon.Daily patterns of phosphate uptake were also rhythmic. At ambient concentrations the assemblage takes up phosphate maximally in the morning while individual cells of the large diatom take it up maximally in the evening.A kinetic analysis of phosphate uptake indicated 2 velocities of uptake for cells of Tabellaria and Fragilaria: a hyperbolic function at small and an apparently linear relationship at relatively large concentrations. The large diatoms, in contrast to the total assemblage, functioned maximally at 2 separate times of the day: in the evening at ambient levels and in the morning at 0.4 μM and larger concentrations.Temporal stratification of the nutrient niche may be achieved by several uptake mechanisms in the algal cell that function at different times of the day or with a variable uptake velocity.

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