Chemoecological investigations of the invasive waterweeds Elodea spp.

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ERHARD, Daniela, 2005. Chemoecological investigations of the invasive waterweeds Elodea spp. [Dissertation]. Konstanz: University of Konstanz

@phdthesis{Erhard2005Chemo-8788, title={Chemoecological investigations of the invasive waterweeds Elodea spp.}, year={2005}, author={Erhard, Daniela}, address={Konstanz}, school={Universität Konstanz} }

Erhard, Daniela 2011-03-24T17:46:28Z eng Chemisch-ökologische Untersuchungen der invasiven Wasserpest Elodea spp. terms-of-use Chemoecological investigations of the invasive waterweeds Elodea spp. application/pdf The invasive waterweeds Elodea nuttallii and E. canadensis contain 7-O-diglucuronides of the flavones luteolin, apigenin and chrysoeriol as well as a phenolic acid similar to caffeic acid. Both species often resemble each other morphologically and may be difficult to distinguish. Consequently, there is a great demand of correct species identification. I present a chemotaxonomic method based on the species-specific flavonoid pattern in Elodea that clearly identified even ambiguous specimens. These had primarily been determined as E. canadensis, but turned out to be E. nuttallii. Especially the ratio between the apigenin- and the chrysoeriol-derivative is characteristic, and my results are in full agreement with molecular taxonomy based on distinct length and base pair polymorphism in the internal transcribed spacer (ITS) region. None of the methods supports evidence for the existence of hybrids between the species, but rather indicate that the distribution of E. nuttallii in Europe is underestimated.<br />The qualitative pattern of flavonoids in different Elodea species is very stable, but their concentrations vary intraspecifically. Flavonoid biosynthesis is in part regulated by external abiotic signals such as light, temperature or resource availability. In first outdoor and laboratory experiments, high light intensities led to a weak accumulation of the phenolic acid and luteolin-7-O-diglucuronide, but in a second experiment no light effect was detectable. However, plants exposed to natural sun light had higher concentrations of either luteolin- or apigenin- and chrysoeriol-glucuronides, indicating that flavonoids exhibit UV protective properties. Temperature might be negatively correlated with the phenolic acid, apigenin- and chrysoeriol-diglucuronide, but additional CO2 supply had no influence at all.<br />Elodea species are often associated with low phytoplankton densities or epiphytic covers. In growth assays with extracts from E. canadensis and E. nuttallii, I demonstrated that allelochemicals can suppress growth of different cyanobacterial culture strains and epiphytic autotrophs isolated from submersed macrophytes. Only Scenedesmus brevispina was stimulated. Bioassay guided fractionation yielded hydrophilic and slightly lipophilic active compounds. Among them are phenolic substances, but neither the phenolic acid nor flavonoids were active. Since growth declined also in a moderately lipophilic fraction of culture filtrate of E. nuttallii, I assume that active compounds are exuded in the water. Allelopathy might thus be relevant in situ and suppress phytoplankton and epiphytes. The differences in the susceptibility of target organisms could (1) at least partly arise from adaptation to the respective host plants and (2) indicate that allelopathic interference might reduce the abundance of some species, especially cyanobacteria, in epiphytic biofilms.<br />Herbivorous larvae of the aquatic moth Acentria ephemerella can severely damage plants like Potamogeton spp. and Myriophyllum spicatum. In contrast, larvae are never found on Elodea nuttallii and avoid feeding on E. canadensis. Using no-choice assays, I showed that E. nuttallii strongly reduces larval growth, independent of culture conditions under which plants were grown. Elodea exposed to high light intensities further increases larval mortality. These results indicate that a negative impact on the fitness of Acentria might be the ultimate reason for the avoidance of Elodea in the field. Neither morphological defences nor nitrogen or phosphorus content of food plants explained these effects, suggesting that allelochemicals (probably flavonoids present in E. nuttallii, but absent in other common host plants of Acentria) are responsible for the reduced growth.<br />Coating Potamogeton leaf disks with Elodea extracts or flavonoids deterred larvae from feeding of this otherwise preferred food source, and yet unknown compounds present in the extracts reduced growth and survival of Acentria. My study is the first, in which larvae were successfully fed with plant secondary metabolites. The concentrations of flavonoids in the assays were at the lower range of concentrations found in the field, indicating that chemical defence in E. nuttallii might be ecologically relevant. The related E. canadensis produces the same flavonoids and might be similarly defended.<br />My studies on the chemical ecology of E. canadensis and E. nuttallii revealed that both species produce allelochemicals, which can assure the access to limiting resources and prevent severe loss of biomass. In contrast to the predictions of the evolution of increased competitive ability (EICA) hypothesis, Elodea spp. thus demonstrate that invasive species might well be chemically defended. This trait can complement their tolerance towards environmental heterogeneity and strengthen the competitive ability of Elodea. 2005 Erhard, Daniela 2011-03-24T17:46:28Z

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