Chemical warfare in freshwater, allelopathic effects of macrophytes on phytoplankton

Contains fulltext : 27378.pdf (publisher's version ) (Open Access)Aquatic macrophytes can excrete chemical substances into their enviroment and these compounds may inhibit the growth of phytoplankton. This process is defined as allelopathy: one organism has effects on another via the excretion of a (mixture of) chemical substance(s). With laboratory and field experiments we studied the allelopathic effects of the aquatic macrophytes, Chara and Stratiotes. Laboratory experiments showed that the aquatic macrophytes had allelopathic effects. Phytoplankton growth was inhibited, some green algae started to form colonies, and algae that received less light were more sensitive to allelopathic substances. Furthermore, differences in the sensitivity of phytoplankton species to allelopathic substances were observed. This may influence the density and composition of (natural) phytoplankton populations. Changes in de dominance of phytoplankton species can also cause changes at higher trophic levels in the food web. The field experiments also gave indications of allelopathy under natural conditions. Phytoplankton (and filamentous algae) densities close to the aquatic macrophytes were often much lower than densities further away from the plants. These observations could not (only) be explained by differences in nutrient concentrations, light intensity and/or grazing. Allelopathy could still have played a role. Field experiments gave indications of allelopathy, but the mystery is not completely solved yet. We need more (field) experiments that show the importance of allelopathy in natural aquatic ecosystems. Another way to study the importance of allelopathy in the field is simulation via a mathematical model. Our model showed that allelopathy may be more important for Stratiotes than it is for Chara. Finally we attempted to chemically identify allelopathic substances from Stratiotes. This identification showed that the substance(s) is/are moderately lipophylic and probably not phenolic.Radboud University, Aquatic Ecology & Environmenta, 31 januari 2006Promotor : Donk, E. van Co-promotor : Smolders, A.J.P.287 p