Long-term effects of warming and nutrients on microbes and other plankton in mesocosms

Authors

  • ARDA ÖZEN,

    1. Department of Biology, Limnology Laboratory, Middle East Technical University, Ankara, Turkey
    2. Department of Biology, Faculty of Science, Ataturk University, Erzurum, Turkey
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  • MICHAL ŠORF,

    1. Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic
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  • CAROLINA TROCHINE,

    1. Department of Bioscience, Aarhus University, Silkeborg, Denmark
    2. Laboratorio de Limnología, Instituto de Investigaciones en Biodiversidad y Medioambiente-Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional del Comahue, Bariloche, Argentina
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  • LONE LIBORIUSSEN,

    1. Department of Bioscience, Aarhus University, Silkeborg, Denmark
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  • MERYEM BEKLIOGLU,

    1. Department of Biology, Limnology Laboratory, Middle East Technical University, Ankara, Turkey
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  • MARTIN SØNDERGAARD,

    1. Department of Bioscience, Aarhus University, Silkeborg, Denmark
    2. Laboratorio de Limnología, Instituto de Investigaciones en Biodiversidad y Medioambiente-Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional del Comahue, Bariloche, Argentina
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  • TORBEN L. LAURIDSEN,

    1. Department of Bioscience, Aarhus University, Silkeborg, Denmark
    2. Sino-Danish Centre for Education and Research (SDC), Beijing, China
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  • LISELOTTE S. JOHANSSON,

    1. Department of Bioscience, Aarhus University, Silkeborg, Denmark
    2. Sino-Danish Centre for Education and Research (SDC), Beijing, China
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  • ERIK JEPPESEN

    1. Department of Bioscience, Aarhus University, Silkeborg, Denmark
    2. Sino-Danish Centre for Education and Research (SDC), Beijing, China
    3. Greenland Climate Research Centre (GCRC), Greenland Institute of Natural Resources, Nuuk, Greenland
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Arda Özen, Department of Biology, Limnology Laboratory, Middle East Technical University, Ankara, Turkey.
E-mail: ardaozen@gmail.com

Summary

1. We followed microbial and other planktonic communities during a 4-month period (February–May) in 12 outdoor flow-through mesocosms designed to elucidate the effect of global warming and nutrient enrichment. The mesocosms were established in 2003.

2. Warming had a smaller effect than nutrients on the biomass of the microbial and planktonic communities, and warming and nutrients together exhibited complex interactions.

3. We did not find direct effects of warming on the biomass of bacterioplankton or ciliates; however, warming significantly added to the positive effect of nutrients on these organisms and on heterotrophic nanoflagellates (HNF). No warming effects on any of the other planktonic groups analysed were detected.

4. The zooplankton: phytoplankton biomass ratio was lowest, and the HNF: bacteria and rotifer: bacteria biomass ratios highest in the heated, nutrient-rich mesocosms. We attribute this to higher fish predation on large-bodied zooplankton, releasing the predation on HNF and competition for rotifers.

5. The proportion of phytoplankton to the total plankton biomass increased with nutrients, but decreased with warming. The opposite pattern was observed for the proportion of phytoplankton to the total microbial biomass.

6. As climate warming may lead to eutrophication, major changes may occur in the pelagic food web and the microbial community due to changes in trophic state and in combination with warming.

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