Taxon-specific primary production of phytoplankton by bio-optical modeling under different conditions of nutrient supply
Final Report Abstract
The measurement of taxon-specific primary production is still an unsolved challenge although it is an important task in explaining the dynamics of natural phytoplankton biodiversity as well as in applied water quality analysis. Traditional methods of measuring primary production (oxygen release or CO2 uptake) are still under debate and do not allow to quantify the relative contribution of the major algal groups to total biomass production. Instead bio-optical modelling is an alternative approach to measure the energy conversion from sunlight into biomass which had been shown to work reliably under lab conditions. In this project it has been studied if this approach can be transferred to real field conditions. This can be done only if it is possible to measure in situ the fraction of the incident light which is absorbed by each taxonomic group selectively and to quantify for each algal group the photosynthetic quantum yield. The basic idea of the project was to use flow cytometry not only to quantify the major algal groups but also to measure their optical properties needed to determine the fraction of light which is harvested by each group. Using PAM fluorometry the photosynthetic quantum yield of each subpopulation was measured. Finally, FTIR spectra of the sorted fractions should allow to mesure the carbon allocation. The results of the project clearly showed that flow cytometry allows to quantify the major groups of the phytoplankton community and to measure the fraction of the incident light which is absorbed by the different subpopulations. The limitation of bio-optical modelling in-situ is the unsolved problem to measure true in-vivo electron transport rates for each of the major taxa. The main problem is that the ratio of fluorescence-based electron transport rates do not match the true biomass formation because the usage of the photosynthetic electrons depends not only on the environmental conditions but also on the taxonomic differences in the metabolic pathways. The approach to use sorted fractions for photosynthetic measurements failed because the sorting procedure strongly impairs the physiological activity. As a surprise it was shown that FTIR spectra can be used to predict in-situ growth rates. This was a new and interesting finding which is now used to refine models which predict the water quality under changing environmental conditions.
Publications
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Fluorescence as a tool to understand changes in photosynthetic electroan flow regulation. In: D. Suggett and O. Prasil (eds), Chlorophyll a fluorescence in Aquatic Sciences: Methods and Applications. Developments in Applied Phycology 4, 75-89, 2010
Peter Ralph, Christian Wilhelm, Johann Lavaud, Torsten Jakob, Katherina Petrou, and Sven Kranz
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The use of FTIR spectroscopy to assess quantitative changes in the biochemical composition of microalgae. J. Biophotonics 3, 557 – 566, 2010
Wagner,H., Stehfest, K, Jakob, T., Langner, U. Wilhelm, C.
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Impact of chlororespiration on non-photochemical quenching of chlorophyll fluorescence and on the regulation of the diadinoxanthin cycle in the diatom Thalassiosira pseudonana. J. Exp. Bot 62, 509-519, 2011
Cruz S, Jakob T, Goss R, Wilhelm C, Leegood R, Horton P
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The impact of cell-specific absorption properties on the correlation of electron transport rates measured by chlorophyll fluorescence and photosynthetic oxygen production in planktonic algae. Plant Physiology and Biochemistry, Vol. 49. 2011, Issue 8, pp.801-808.
Ulrich Blache, Torsten Jakob, Wanwen Su, Christian Wilhelm
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Different phycobilin antenna organisations affect the balance between light use and growth rate in the cyanobacterium Microcystis aeruginosa and in the cryptophyte Cryptomonas ovata.
Photosynthesis Research, Vol. 111, Issue 1-2, pp. 173-183.
Kunath, C. et al.
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FTIR spectra of algal species can be used as physiological fingerprints to assess their actual growth potential.
Physiologia Plantarum, Volume 146. 2012, Issue 4, pp. 427–438.
Christian Jebsen, Alessandra Norici, Matteo Palmucci, Mario Giordano, Christian Wilhelm
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Sub-community FTIR to determine physiological cell states.
Current Opinion in Biotechnology, Vol. 24. 2013, Issue 1, P.. 88–94.
Wagner , H. et al.
