Contrôle de l’activité photosynthétique du phytoplancton en milieu côtier : utilisation de la fluorescence spectrale et de la fluorimétrie modulée

Abstract : Dynamics of phytoplankton photosynthetic activity were characterised in a macrotidal coastal ecosystem (the Strait of Dover, eastern English Channel) and related to environmental conditions. Spatial and temporal variability of photosynthetic parameters were studied at different scales, between September 2008 and August 2010. The level of variability and controlling factors of photosynthetic parameters depend on the scale considered. In space, no gradient of photosynthetic parameters was found between coastal and offshore waters. By contrast, within the water column, variations of the maximum quantum yield (Fv/Fm), the maximum electron transport rate (ETRm) and the light saturation coefficient (Ek) in relation to the light history of cells were observed. At short time scale (from hour to the scale of a neap-spring tide cycle), considerable variations of photosynthetic parameters were observed. Light conditions, temperature and nutrient availability were the main controlling factors. At longer time scale (from fortnightly to inter-annual scales), Fv/Fm, α (the maximal light utilization efficiency) and ETRm varied without any clear seasonal cycle. By contrast, Ek followed the seasonal variations of light except during summer where its changes of Ek were small compared to the light variability. At these time scales, close interplays between shifts of phytoplankton communities and changes of light, temperature and nutrient availability controlled the variability of photosynthetic parameters.
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Emilie Houliez. Contrôle de l’activité photosynthétique du phytoplancton en milieu côtier : utilisation de la fluorescence spectrale et de la fluorimétrie modulée. Biodiversité et Ecologie. Université de Lille 1, 2012. Français. ⟨tel-01084544⟩

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