Funktioneller Zusammenhang zwischen der Biodiversität des Phytoplanktons und dessen Nahrungsqualität für das herbivore Zooplankton
Zusammenfassung der Projektergebnisse
Research on species diversity has become increasingly important over the past years, as anthropogenic influences (including climate change and eutrophication) result in strong challenges ecosystems face. In aquatic systems, shifts in phytoplankton species may change food supply for the consumer radically. The beneficial impact on species diversity, the resulting resource use efficiency, and the benefits for the consumer have been previously shown. However, the underlying mechanisms remained unclear. Unselective filter feeders such as Daphnia ingest whole phytoplankton cells, and hence, receive packages of possibly different food quality. Generally, phytoplankton species produce lipids to different extent, which is additionally influenced by environmental conditions. This is making it more difficult to unravel how biodiversity, environmental conditions, and consumer life history correspond. We anticipated resolving this interplay at different trophic levels: phytoplankton and zooplankton. Phytoplankton communities that were cultured in lab experiments, had different diversity levels, and were competing for resources (nutrients and/ or light), resulting in semi-natural communities. These represented possible food sources for zooplankton. The zooplankton was then exposed to some of these communities or specific species and their growth rates were examined. We confirmed that interspecific competition does result in higher concentrations of ecologically and physiologically relevant long-chained polyunsaturated fatty acids (e.g., eicosapentaenoic acid) than expected based on monocultures (result 1). We further investigated how far the variability in biochemical nutrients within the primary produces depends on their heterogeneous responses to environmental factors (results 2 and 3) for a deeper understanding of the response of aquatic consumers to changing environmental conditions and losses in species richness/diversity. The important mechanisms in shaping phytoplankton communities species sorting and physiological plasticity are determined by environmental conditions (result 2). When nutrients were limiting species sorting (changes of the species composition) was more relevant, whereas at sufficient nutrient supply species were able to engage in physiological plasticity (changes of fatty acid profile) based on light intensity and condition. Additionally, indication of food quality was dependent on phosphorous and light condition, emphasizing the importance of multifactorial studies on the phytoplankton community level for zooplankton consumers. We deepened this understanding by inspecting the physiology of these phytoplankton communities further (result 3). The response of phytoplankton at different time scales to environmental conditions and variability showed that communities can to some extent compensate for light variability in the fast response of photosynthetic activity by adaptation in the intermediate response of pigment composition, which was very pigment-specific. In the slow response of biomass and species composition effects seemed little, but species-specific. How important species identity (or taxonomic identity) is was seen when Daphnia were fed with different phytoplankton communities (result 4). On one hand a general increase of species diversity, resulted in an increase of fatty acid diversity, and increased Daphnia growth. On the other hand, Daphnia were co-limited by sterols and polyunsaturated fatty acids, when diets consisted of cyanobacteria-dominated communities. Most cyanobacteria are generally of low food quality (no PUFA or sterols), however, even in cyanobacteria dominated eutrophic lakes consumers have the possibility to evolve to cope with the circumstances (result 5). In conclusion, it is difficult to disentangle the effects of environmental conditions and diversity on phytoplankton communities and possible effects for Zooplankton consumers. Here, we advanced the field by using conservative biodiversity indices applied on different response variables that are crucial for understanding phytoplankton community development and consumer performance.
Projektbezogene Publikationen (Auswahl)
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2015. Interspecific competition in phytoplankton drives the availability of essential mineral and biochemical nutrients. Ecology 96(9): 2467-2477
Wacker, A., V. Marzetz, & E. Spijkerman
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2015. Photosynthetic and fatty acid acclimation of four phytoplankton species in response to light intensity and phosphorus availability. European Journal of Phycology 50(3): 288-300
Wacker, A., M. Piepho, & E. Spijkerman
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2016. Light induced changes in fatty acid profiles of specific lipid-classes in freshwater phytoplankton. Frontiers in Plant Science 7: 264
Wacker, A., M. Piepho, J.L. Harwood, I.A. Guschina, & M.T. Arts
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2017. Ecophysiological strategies for growth at varying light and organic carbon supply in two species of green microalgae differing in their motility. Phytochemistry 144: 43-51
Spijkerman, E., M. Lukas, & A. Wacker
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2017. Linking primary producer diversity and food quality effects on herbivores: A biochemical perspective. Scientific Reports 7: 11035
Marzetz, V., A-M. Koussoroplis, D. Martin-Creuzburg, M. Striebel, & A. Wacker
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2019. Nitrate or ammonium: Influences of nitrogen source on the physiology of a green alga. Ecology and Evolution 9: 1070-1082
Lachmann, S.C, T. Mettler-Altmann, A. Wacker, & E. Spijkerman
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2020. Phytoplankton community responses to interactions between light intensity, light variations, and phosphorus supply. Frontiers in Environmental Science
Marzetz, V., E. Spijkerman, M. Striebel, & A. Wacker
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Evaluating the relevance of species sorting and physiological plasticity of phytoplankton communities grown in a multifactor environment. Freshwater Biology
Marzetz, V. & A. Wacker
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2022. A sterol-mediated gleaner-opportunist trade-off underlies the evolution of grazer resistance to cyanobacteria. Proceedings of the Royal Society B
Isanta-Navarro, J., T. Klauschies, A. Wacker & D. Martin-Creuzburg
