AME 79:235-245 (2017)  -  DOI:

The functional role of planktonic mixotrophs in altering seston stoichiometry

Stefanie D. Moorthi1,*, Robert Ptacnik2, Robert W. Sanders3, Robert Fischer1, Michaela Busch1, Helmut Hillebrand1

1Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, Schleusenstra├če 1, 26382 Wilhelmshaven, Germany
2WasserCluster Lunz, Biologische Station GmbH, Dr. Carl Kupelwieser Promenade 5, 3293 Lunz am See, Austria
3Temple University, Department of Biology, 1900 N. 12th Street Philadelphia, PA 19122, USA
*Corresponding author:

ABSTRACT: Mixotrophic protists are widespread and relevant primary producers and consumers in planktonic food webs. Given their dual mode of nutrition, mixotrophs face different constraints in allocating resources to cellular structures compared to strict photoautotrophs. However, little is known about their stoichiometric requirements and their flexibility in nutrient content and thus food quality, or how this affects consumer performance and nutrient recycling. In the present study, we tested for systematic differences in elemental composition between photoautotrophic and mixotrophic protists. We compiled intracellular nutrient ratios of mixotrophic and phototrophic species from culture experiments and from 2 lake surveys. Overall, both laboratory and field data indicated that mixotrophy has a stabilizing effect on the nutrient stoichiometry of primary producers under changing nutrient supply. In laboratory experiments, mixotrophs showed a lower variability in intracellular N:P ratios compared to strict phototrophs and were more stable in their elemental composition in response to a gradient of dissolved N:P availability. With increasing contributions of mixotrophic phytoplankton taxa to total lake phytoplankton, both the mean and variance in seston C:P ratios decreased, i.e. communities with higher proportion of mixotrophs overall exhibited more constrained seston stoichiometry. Our results show that mixotrophy may have direct implications for nutrient cycling and secondary production through regulation of seston stoichiometry, buffering stoichiometric constraints for herbivores and enabling a more stable secondary production compared to systems dominated by phototrophic specialists.

KEY WORDS: Mixotrophy · Stoichiometry · Nutrients · Food quality · Trophic transfer · Trophic efficiency · Plankton food web

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Cite this article as: Moorthi SD, Ptacnik R, Sanders RW, Fischer R, Busch M, Hillebrand H (2017) The functional role of planktonic mixotrophs in altering seston stoichiometry. Aquat Microb Ecol 79:235-245.

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