Microbial dynamics in autotrophic and heterotrophic seawater mesocosms. I. Effect of phytoplankton on the microbial loop

Abstract : The effect of phytoplankton on the other compartments of a simple microbial loop consisting of dissolved matter, bacteria and nanoflagellates was investigated in three 1000 1 mesocosms. These mesocosms were inoculated with a natural bacterial community and (1) no other additions (No Addition tank), (2) Phaeocystis globosa (Phaeocystis tank), or (3) 2 diatom species (Diatom tank). During the 20 d experiment, autotrophic activity was negligible in the No Addition tank. In contrast a small P. globosa bloom developed in the Phaeocystis tank and a large diatom bloom dominated the Diatom tank. In this paper we describe the experiment, the changes in chlorophyll a and heterotrophic nanoflagellate concentrations, as well as the cycling of nitrogen, phosphorus, and silica. Then we provide a synthesis of the structure and functioning of the microbial loops in these 3 systems using cluster analysis, a statistical pattern recognition tool. The goal was to test the hypothesis that differences in the resident phytoplankton populations would be reflected in (1) the composition and concentration of dissolved organic matter, (2) the composition of the bacterial community, (3) the food web, and (4) the cycling of elements and organic matter. In all 3 mesocosms, nitrate and silicic acid remained abundant. Orthophosphate was preferred by diatoms, whereas Phaeocystis appeared to prefer dissolved organic phosphorus. The hypothesis that phytoplankton composition shapes the structure and functioning of the microbial loop was partially supported: 6 d after inoculation each mesocosm exhibited a distinct organic matter signature. After 10 to 12 d, concentrations of heterotrophic nanoflagellates were high enough to exert significant grazing pressure in all 3 mesocosms. A parallel shift in bacterial community composition was visible in all mesocosms at this time, possibly reflecting grazing pressure. The food-web structure developed divergently in the 3 mesocosms during the second half of the experiment. Differences in biochemical cycling between mesocosms were predominantly driven by the large quantitative differences in autotrophs.
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Article dans une revue
Aquatic Microbial Ecology, Inter Research, 2007, 49 (2), pp.109-121. 〈10.3354/ame01138〉
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Contributeur : Christina De La Rocha <>
Soumis le : vendredi 26 mars 2010 - 10:53:53
Dernière modification le : jeudi 11 janvier 2018 - 06:22:24

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Uta Passow, Christina De La Rocha, Carol Arnosti, H.-P. Grossart, Alison E. Murray, et al.. Microbial dynamics in autotrophic and heterotrophic seawater mesocosms. I. Effect of phytoplankton on the microbial loop. Aquatic Microbial Ecology, Inter Research, 2007, 49 (2), pp.109-121. 〈10.3354/ame01138〉. 〈hal-00467179〉

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