AME 49:143-156 (2007)  -  doi:10.3354/ame01140

Microbial dynamics in autotrophic and heterotrophic seawater mesocosms. III. Organic matter fluxes

Hans-Peter Grossart1,*, Anja Engel2, Carol Arnosti3, Christina L. De La Rocha2, Alison E. Murray4, Uta Passow2

1Institute of Freshwater Ecology and Inland Fisheries, Dept. of Limnology of Stratified Lakes, Alte Fischerhütte 2, 16775 Stechlin, Germany
2Alfred-Wegner-Institut für Polar- und Meeresforschung, Am Handelshafen 12, 27570 Bremerhaven, Germany
3Department of Marine Sciences, University of North Carolina, Chapel Hill, North Carolina 27599-3300, USA
4Division of Earth and Ecosystem Science, Desert Research Institute, 2215 Raggio Parkway, Reno, Nevada 89512, USA

ABSTRACT: We monitored the dynamics of extracellular organic matter in 3 mesocosms: one dominated by a heterotrophic (microbial) community with negligible autotrophic activity (net heterotrophic system), a second where a small Phaeocystis bloom developed (production and loss almost balanced), and a third harboring a large diatom bloom (net autotrophic system). In all mesocosms, meso- and macroscopic heterotrophic organisms were excluded to primarily study extracellular organic matter production and turnover by specific algae and microbial loop organisms, respectively. Concentration and composition of dissolved organic matter (DOM), i.e. dissolved organic carbon (DOC), monosaccharides and total carbohydrates (MCHO and TCHO), free and combined neutral carbohydrates (DFCHO and DCCHO), as well as free and combined amino acids (DFAA and DCAA) were measured. In addition, net and gross community production rates were determined to calculate C-budgets. Whereas concentrations and composition of MCHO differed very little among the 3 mesocosms, dynamics of TCHO, DFCHO, and DCCHO differed significantly. Concentrations of DFAA were higher in both algal mesocosms compared to the heterotrophic system, and composition of DFAA was significantly different in the Phaeocystis and Diatom tanks. The composition and concentration of DCAA, however, were similar in all 3 mesocosms. Total dissolved carbohydrates and amino acids comprised a substantial fraction of the DOC pool. Dynamics of these DOC fractions, however, could only partly explain those of DOC, implying either that other dissolved compounds were important for overall C-cycling, or that microbial degradation of DOM affects the detection of carbohydrates and protein components.


KEY WORDS: Mesocosms · Organic carbon · Amino acids · Carbohydrates · Enzymes ·Carbon budgets


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Cite this article as: Grossart H, Engel A, Arnosti C, De La Rocha CL, Murray AE, Passow U (2007) Microbial dynamics in autotrophic and heterotrophic seawater mesocosms. III. Organic matter fluxes. Aquat Microb Ecol 49:143-156

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