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(W/EH114) Does the Phytoplankton React to Exudates of Cyanobacteria ? Allelopathic Effects of Cyanobacterial Toxins. Noack, Udo1, Kutzner, Ute1, Scheerbaum, Dirk1, 1 ABSTRACT- Allelopathic effects are defined as stimulating and inhibiting interactions of plants, fungi and bacteria caused by the exudation of biochemically active substances. The exudation rates of allelochemicals correlate with trophic important parameters e.g. total phosphate and nitrogen. Furthermore there are some cellular compounds with allelopathic effects and their content corresponds to nutrient situation and growth rate. Allelochemicals e.g. cyanobacterial toxins have an influence on the abundance of other species and therefore on the succession in aquatic ecosystems. They should be considered as the result of ecologi-cal and physiological strategies for nutrients and biotopes. The majority of the documented allelopathic interactions are inhibiting effects but stimulating effects have also been observed. Allelochemicals con-sist of organic compounds that often have lipophilic properties with the ability to pass biological mem-branes. Laboratory investigations on allelopathic interactions may not be compared with field studies. Interactions of allelochemicals with dissolved organic compounds may lead to decreased allelopathic effects. Laboratory simulated successions often not correspond to the natural successions. In mono-species test designs diversities, abundances and the nutrient situation are not comparable to field eco-systems. Cyanobacterial species were tested in ecotoxicity studies. The results will be presented. Key words: Cyanobacteria, Exudates, Allelopathic Substances, Toxins |
