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Mixotrophic organisms become more heterotrophic with rising temperature

Authors

  • Susanne Wilken,

    Corresponding author
    1. Aquatic Microbiology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands
    • Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands
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  • Jef Huisman,

    1. Aquatic Microbiology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands
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  • Suzanne Naus-Wiezer,

    1. Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands
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  • Ellen Van Donk

    1. Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands
    2. Department of Ecology and Biodiversity, University of Utrecht, Utrecht, The Netherlands
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Correspondence: E-mail: s.wilken@nioo.knaw.nl

Abstract

The metabolic theory of ecology predicts that temperature affects heterotrophic processes more strongly than autotrophic processes. We hypothesized that this differential temperature response may shift mixotrophic organisms towards more heterotrophic nutrition with rising temperature. The hypothesis was tested in experiments with the mixotrophic chrysophyte Ochromonas sp., grown under autotrophic, mixotrophic and heterotrophic conditions. Our results show that (1) grazing rates on bacterial prey increased more strongly with temperature than photosynthetic electron transport rates, (2) heterotrophic growth rates increased exponentially with temperature over the entire range from 13 to 33 °C, while autotrophic growth rates reached a maximum at intermediate temperatures and (3) chlorophyll contents during mixotrophic growth decreased at high temperature. Hence, the contribution of photosynthesis to mixotrophic growth strongly decreased with temperature. These findings support the hypothesis that mixotrophs become more heterotrophic with rising temperature, which alters their functional role in food webs and the carbon cycle.

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