Aquatic Sciences Meeting, Albuquerque 2001

SS13 Mixotrophic Plankton - Combining Phototrophic and Heterotrophic Nutrition

Date: Friday, February 16, 2001, Time: 9:15:00 AM

Location: Acoma/Zuni/Tesuque

Tittel, J, , Universität Potsdam, Potsdam, Germany, tittel@rz.uni-potsdam.de

Bissinger, V, , Universität Potsdam, Potsdam, Germany, vbissing@rz.uni-potsdam.de

Zippel, B, , UFZ, Department of Inland Water Research, Magdeburg, Germany, zippel@gm.ufz.de

Knösche, R, , Universität Potsdam, Potsdam, Germany, knoesche.pdm.eiche@t-online.de

Gaedke, U, , Universität Potsdam, Potsdam, Germany, gaedke@rz.uni-potsdam.de

Winkler, M, , UFZ, Department of Inland Water Research, Magdeburg, Germany, winkler@gm.ufz.de

WHY DO MIXOTROPHS DOMINATE THE PLANKTON IN ACIDIC MINING LAKES

Lakes formed in coal mining pits often undergo acidification due to pyrite weathering. They are highly mineralized (conductivity 2 mS) and characterized by clear, deeply colored water, low pH (2.5-3.5) and high iron and sulfate concentrations (150 and 1300 mg/L, respectively). Pigmented flagellates constituted at least 90 % of autotrophic biomass. Ochromonas was abundant in near surface layers despite tenfold higher bacterial densities at larger depth. Dilution experiments indicated ingestion of Chlamydomonas if present at high densities. Chlamydomonas dominated in the depth, forming persistent peaks at low light intensities (0.2-0.02% of surface light). Batch experiments using isolated Chlamydomonas and filtered lake water at 16 °C revealed no photosynthetic growth below 1% of surface light at noon. DOC entered the lake with inflowing groundwater and was high in deeper layers. DOC stimulated growth of both flagellates in situ. Mixotrophy is frequently regarded as adaptation to highly variable environmental conditions. As the latter are relatively stable in our systems we hypothesize that mixotrophy rather provides a successful strategy to compensate enhanced metabolic costs in our adverse environments.

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Aquatic Sciences Meeting, Albuquerque 2001

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