Evolution of the scattering properties of phytoplankton cells from flow cytometry measurements Article - Juillet 2017

William Moutier, Lucile Duforêt-Gaurier, Melilotus Thyssen, Hubert Loisel, Xavier Meriaux, Lucie Courcot, David Dessailly, Anne-Hélène Rêve, Gérald Grégori, Séverine Alvain, Aude Barani, Laurent Brutier, Mathilde Dugenne, Lakshminarayana Polavarapu

William Moutier, Lucile Duforêt-Gaurier, Melilotus Thyssen, Hubert Loisel, Xavier Meriaux, Lucie Courcot, David Dessailly, Anne-Hélène Rêve, Gérald Grégori, Séverine Alvain, Aude Barani, Laurent Brutier, Mathilde Dugenne, Lakshminarayana Polavarapu, « Evolution of the scattering properties of phytoplankton cells from flow cytometry measurements  », PLoS ONE, juillet 2017. ISSN 1932-6203

Abstract

After the exponential growth phase, variability in the scattering efficiency of phytoplankton cells over their complete life cycle is not well characterised. Bulk measurements are impacted by senescent cells and detritrus. Thus the analysis of the evolution of the optical properties thanks to their morphological and/or intra-cellular variations remains poorly studied. Using the Cytosense flow cytometer (CytoBuoy b.v., NL), the temporal course of the forward and sideward efficiencies of two phytoplankton species (Thalassiosira pseudonana and Chlamydomonas concordia) were analyzed during a complete life-cycle. These two species differ considerably from a morphological point of view. Over the whole experiment, the forward and sideward efficiencies of Thalassiosira pseudonana were, on average, respectively 2.2 and 1.6 times higher than the efficiencies of Chlamydomonas concordia. Large intra-species variability of the efficiencies were observed over the life cycle of the considered species. It highlights the importance of considering the optical properties of phytoplankton cells as a function of the population growth stage of the considered species. Furthermore, flow cytometry measurements were combined with radiative transfer simulations and biogeochemical and optical measurements. Results showed that the real refractive index of the chloroplast is a key parameter driving the sideward signal and that a simplistic two-layered model (cytoplasm-chloroplast) seems particularly appropriate to represent the phytoplankton cells.

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