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Écologie et fonctionnement des communautés lichéniques saxicoles-hydrophiles

Abstract : Algae and fungi have formed lichens by symbiotic association, which, due to their ecological amplitude, have been able to colonise all environments. We propose that lichens subject to periods of immersion in river water be called "hydrophilic". The floristic compositions of hydrophilic lichen communities were defined by the annual duration of their immersion. The sub-hydrophilic groups were immersed for less than three months, the meso-hydrophilic groups for more than three months and less than ten months and finally the hyper-hydrophilic groups were immersed for more than ten months of the year. A phytosociological schema was created, based on three hundred surveys conducted by the integral sampling method. The lichens present at the various levels of embedment and river altitude form a class comprising of three phytosociological orders, characterised by the annual duration of immersion. Two alliances are defined for each of these orders, by bioclimatic stage. For each of these six alliances there are associations of several lichens, which are defined by their biotic characteristics. Due to their frequency of immersion and the significance of their recovery, four "model" lichens were selected (one aerial and three hydrophilic species). For the first time with regards to hydrophilic lichens, the flow of CO2 and O2 were quantified under different lighting, aquatic and aerial. Photosynthetic pigments and ergosterol were valued; the photochemical potential ( PSII) response to the rate of hydration was qualified. The photosynthetic and respiratory activity of the hydrophilic lichens is comparable to the literature on aerial lichens. The hydrophilic lichens present rapid hydration-dehydration kinetics during transitions between immersion and exposure.  PSII proves to be very sensitive to these transitions. For all of the functions studied, significant differences appeared between the hyper and sub-hydrophilic lichens, whilst the meso-hydrophilic lichens behaved intermediately. Our results constitute the first ecological and functional characterisation of hydrophilic lichens. They will certainly be exploited and developed in order to provide a better understanding of the role of lichens in land surface colonisation by phanerogams.
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Submitted on : Friday, October 26, 2012 - 2:30:36 PM
Last modification on : Monday, April 5, 2021 - 2:26:12 PM
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  • HAL Id : tel-00745808, version 1

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Clother Coste. Écologie et fonctionnement des communautés lichéniques saxicoles-hydrophiles. Biodiversité et Ecologie. Université Paul Sabatier - Toulouse III, 2011. Français. ⟨tel-00745808⟩

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