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Impact of elevated pCO2 on optical properties of the coccolithophorid Emiliania huxleyi grown under nitrate limitation
Denis, Michel; Sciandra, Antoine; Harlay, Jérôme et al.
2003EGS-AGU-EUG Joint Assembly
 

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Abstract :
[en] Side scatter and red fluorescence properties of the coccolithophore Emiliania huxleyi were investigated when NO3-limited continuous cultures were submitted to a CO2 partial pressure (pCO2) increase from 400 to 700 ppm. Cultures renewed at the rate of 0.5 d-1 and were submitted to saturating light level. pCO2 was controlled by bubbling CO2-rich or CO2- free air in the cultures. Side scatter of a single cell is considered to reflect not only its overall shape but mainly its inner structure and content through a complex combination of optical properties including absorption, diffusion, refractive index and refraction. Consequently, the cultures of Emiliania huxleyi were monitored by flow cytometry to detect possible changes in its optical properties at the single cell level under the effect of CO2 doubling in the atmospheric phase. The average SD for counting 5 replicates was less than 1.6% over the period of the study. It was 0.1 and 0.2% for fluorescence and side scatter respectively. Considering the possible decalcification induced by the increase of CO2 in the chemostat atmosphere, the maximum variation that can be expected for side scatter is that provided by the coccolith depletion upon acidification of the cell suspension. The acidification induced a large (36%) decrease of the side scatter signal as expected and had no detectable effect on the red fluorescence. To validate the assignment of this change on coccolith dissolution, the same experiment was repeated with a culture of a non-calcifying species, Dunaliella tertiolecta. The acidification of D. tertiolecta suspension induced no detectable change, both on fluorescence and side scatter. During the time of the experiment, the decline of side scatter never approached the potential 36% change observed when coccoliths are fully dissolved. Interestingly, the specific chl a fluorescence of E. huxleyi slightly increased during the period of high CO2 level. At the end of the experiment this increase amounted to 2.8% of the initial signal. The average SD of red fluorescence being 0.1%, this increase must be considered as significant. Furthermore, it progressed linearly with time over the period of observation. However, the experiment did not last enough to know if the fluorescence increase had already reached its maximum value. The acidification experiment supported the use of side scatter as a relevant parameter to trace potential changes in calcification. Since the estimated 25% decrease in calcification induced by the rise in CO2 atmosphere did not result in dramatic changes in side scatter values, we can conclude that the number of coccoliths and the overall shape and granulosity of cells was not significantly affected by this decrease. Changes must have only affected tiny structure details of the coccoliths like those observed on published electron micrographs. The small but significant increase of the fluorescence signal can be considered as a physiological response to the CO2 rise. This suggests a more dynamic photosynthetic process that would result in a higher rate of organic matter production providing that the system is not nutrient limited as in the present situation.
Disciplines :
Environmental sciences & ecology
Aquatic sciences & oceanology
Author, co-author :
Denis, Michel;  Laboratoire d’Océanographie et de Biogéochimie, Centre d'Océanologie de Marseille, Université Mixte de Recherche (UMR) 6535, Centre National de la Recherche Scientifique (CNRS)-Université de la Méditerranée, Case 901, 13288 Marseille Cedex 9, France
Sciandra, Antoine;  Laboratoire d’Océanographie, Université Mixte de Recherche (UMR) 7093, Centre National de la Recherche Scientifique- Université Pierre et Marie Curie (CNRS-UPMC), BP 28, 06234 Villefranche-sur-mer Cedex, France
Harlay, Jérôme ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Océanographie chimique
Lefèvre, Dominique;  Laboratoire d’Océanographie et de Biogéochimie, Centre d'Océanologie de Marseille, Université Mixte de Recherche (UMR) 6535, Centre National de la Recherche Scientifique (CNRS)-Université de la Méditerranée, Case 901, 13288 Marseille Cedex 9, France
Lemée, Rodolphe;  Laboratoire d’Océanographie, Université Mixte de Recherche (UMR) 7093, Centre National de la Recherche Scientifique- Université Pierre et Marie Curie (CNRS-UPMC), BP 28, 06234 Villefranche-sur-mer Cedex, France
Rimmelin, Peggy;  Laboratoire d’Océanographie et de Biogéochimie, Centre d'Océanologie de Marseille, Université Mixte de Recherche (UMR) 6535, Centre National de la Recherche Scientifique (CNRS)-Université de la Méditerranée, Case 901, 13288 Marseille Cedex 9, France
Gattuso, Jean-Pierre;  Laboratoire d’Océanographie, Université Mixte de Recherche (UMR) 7093, Centre National de la Recherche Scientifique- Université Pierre et Marie Curie (CNRS-UPMC), BP 28, 06234 Villefranche-sur-mer Cedex, France
Language :
English
Title :
Impact of elevated pCO2 on optical properties of the coccolithophorid Emiliania huxleyi grown under nitrate limitation
Publication date :
06 April 2003
Event name :
EGS-AGU-EUG Joint Assembly
Event organizer :
http://www.egu.eu/
Event place :
Nice, France
Event date :
6-11 April 2003
Audience :
International
Available on ORBi :
since 06 January 2011

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