Growth and photosynthesis of the endemic Mediterranean deep-water kelp Laminaria rodriguezii along temperature and irradiance gradients


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Inka.Bartsch [ at ] awi.de

Abstract

The limit of the euphotic zone is characterized by multiple abiotic forcing acting simultaneously on the organisms. The endemic kelp Laminaria rodriguezii manages to survive and develop large populations of ecological importance in this habitat, under very low light conditions (2-3 μmol photon m-2 s-1). Examples of deep-water photosynthetic species helped to establish physiological characteristics of this low-light adaptation. This study investigated whether these prerequisites were present in juvenile sporophytes of L. rodriguezii, investigating relative growth rate (RGR) and photosynthetic performances along an irradiance gradient, in a laboratory experiment. The effect of temperature on growth was also analyzed. Determination of the RGRs, the characteristics of the photosynthetic apparatus, pigment contents as well as the general structure of the thallus over 14 days showed that all experimental factors affected the physiology and the morphology of the sporophytes. A growth optimum at 10-20 °C was found as well as a growth-saturating irradiance of 12 μmol photon m-2 s-1. Despite a reduced photosynthetic activity (PO2), the L. rodriguezii ‘sporophytes managed to maintain high photosynthetic efficiency (α), lower saturating irradiance (Ik) and high chlorophyll levels to optimize the absorption of photons from the small portion of light perceived at such depths. Coupled with reduced respiration due to the low surrounding temperature (13 °C), very diminished but positive growth at the lowest irradiances (1-3 μmol photon m-2 s-1) is possible. Surprisingly, higher RGR and PO2 were observed in high irradiance treatments demonstrating some photoacclimation capacity. Nevertheless, these high light conditions still cause dynamic photoinhibition (low FV/FM ratio). Ours results suggest that Laminaria rodriguezii is indeed a species adapted to low-light but further studies are needed to fully understand the biology of this endemic kelp, now endangered by human activities.



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Thesis (Master)
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Not peer-reviewed
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Published
Eprint ID
52235
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Pageault, L. (2020): Growth and photosynthesis of the endemic Mediterranean deep-water kelp Laminaria rodriguezii along temperature and irradiance gradients , Master thesis, Alfred-Wegener-Institut and Institut Pyhtéas Aix-Marseille Université.


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