Dr. Susanne Dunker
Department for Physiological Diversity
German Center for Integrative Biodiversity Research (iDiv)
Deutscher Platz 5a
phone: +49 341 9733170
My research interests are strongly influenced by the time of my diploma thesis, where I dealt with a hypertrophic lake in Leipzig. In this lake cyanobacterial blooms and fish kill occurred. I am fascinated by the fact that although a lake contains extensive nutrients, during the phase of cyanobacterial blooms, diversity of other phytoplankton species is very low. I want to gain insights into which factors make it possible that diversity is suppressed and reversed, under which circumstances diversity can be supported.
Phytoplankton organisms are ideal candidates to study diversity due to their fast growth. These organisms are microscopic small but have an enormous impact on the water quality and ecology. Their ability to convert light energy to biomass via photosynthesis determines the extent of primary production. The efficiency of this conversion (numbers of photons needed to assimilate one molecule of carbon) is an important trait for physiological activity and highly varies within taxonomic groups (e.g. cyanobacteria, green algae, dinophytes, cryptophytes and diatoms). This means that the same quantity of light not necessarily leads to the same productivity for different taxa. Until now, it was not possible to investigate the respective energy use efficiency of different taxa in a complex community. The aim of my PhD-thesis was to use cellular characteristics to resolve the energy use efficiency for different species in a mixed culture.
Phytoplankton species can be distinguished due to their different pigmentation patterns by the means of flow cytometry. Flow cytometry delivered the following cellular traits: cell volume, dry weight and chl a-content per cell and also the variability of these traits within a population. These data allowed the quantification of absorbed light energy in relation to assimilated biomass separately for different species in a mixed culture. I could show that energy use efficiency differed between mono-culture- and co-culture-conditions in a species-specific manner. This means that co-cultivation could be less productive in comparison to the mono-cultures because within the co-culture one species had a lower energy-use-efficiency.
With this work I demonstrated, how energy is distributed and converted to biomass in a phytoplankton community. Furthermore, a model system for competition experiments was established (Dunker et al. 2013). Now it is possible to consider aspects like different cell size, the influence of nutrient-concentrations or different defense traits like morphological and chemical defense with regard to the outcome of competition. It is also possible to examine multi-species experiments if the used species differ enough in their pigmentation to guarantee a fast identification by flow cytometry.
|04/2015 - present||present Post-Doc at UFZ (Helmholtz centre for environmental research)/ iDiv (German Centre for Integrative Biodiversity Research) Leipzig, Germany|
|10/2013 - 03/2015||Post-Doc at the University of Leipzig (“Plant Physiology”), Germany|
|12/2008 - 07/2013||
PhD thesis at the University of Leipzig, Germany
Institute of Biology, Department: “Plant Physiology”
Title: “Dynamic of phytoplankton under hypertrophic conditions”
Supervisor: Prof. Dr. C. Wilhelm
|10/2003 - 10/2008||Study of Biology (University of Leipzig, Germany)|
During the time of my PhD thesis, I gained a lot of experience in the field of algal culturing, flow cytometry, HPLC, R-programming, image analysis and publication. Additionally, I was involved in water quality monitoring of a hypertrophic lake (Lake Auensee, Leipzig) and, therefore, I also gained experiences in field work, which was of great advance to establish suitable culturing conditions in the laboratory. Because I am fascinated by phytoplankton succession and the underlying causes I developed a dominance-analysis-tool to extract habitat templates in the sense of Reynolds (1998) for different phytoplankton groups for Lake Auensee from the monitoring period 2002-2011 (For chlorophytes a habitat template is shown in the left). These results can be used for mesocosm experiments to validate the obtained optimal growth conditions especially with regard to N:P stoichometry.
As an important finding of my PhD-thesis, I have discovered that productivity in a mixed culture could be lowered, in comparison to mono-cultures. A reason for this reduced biomass assimilation could be an excretion of organic carbon. At the moment, I am trying to establish a method to evaluate a profile of extracellular carbon, to explain if carbon excretion is induced by allelochemicals, leading to a strong dominance of cyanobacteria.
During my PhD thesis, I could show that species-specific energy use efficiency is a good trait for eco-physiological fitness, reflecting light absorption and photosynthesis efficiency, as well as metabolic activity. This knowledge can be used to test if this trait, measurable by cellular characteristics, is suitable to mirror both, productivity and diversity.
With the experimental set-up I also want to examine the trade-off between competitiveness and grazing resistance. For this I would choose several species known for different grazing defense strategies like chemical defense (Microcystis aeruginosa) and morphological defense (Scenedesmus obliquus). While chemical defense will not have an influence on cell size (high competitiveness), a morphological defense (larger particles) can be achieved by lower metabolic costs, but at the same time competitiveness is reduced. Competition experiments with these species (Scenedesmus obliquus, Microcystis aeruginosa) will be quite interesting. I am also interested on an upscaling of trait-diversity relationships on multispecies levels, as well as on higher plants.