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Aquatic Microbial Ecology

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AME 37:265-281 (2004)  -  doi:10.3354/ame037265

Temperature effects on respiration and photosynthesis in three diatom-dominated benthic communities

Kasper Hancke1,2,*, Ronnie N. Glud1

1Marine Biological Laboratory, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark
2Present address: Trondhjem Biological Station, Norwegian University of Science and Technology, 7491 Trondheim, Norway

ABSTRACT: Short-term temperature effects on respiration and photosynthesis were investigated in intact diatom-dominated benthic communities, collected at 2 temperate and 1 high-arctic subtidal sites. Areal rates of total (TOE) and diffusive (DOE) O2 exchange were determined from O2-microsensor measurements in intact sediment cores in the temperature range from 0 to 24°C in darkness and at 140 µmol photons m-2 s-1. In darkness, the O2 consumption increased exponentially with increasing temperature for both TOE and DOE, and no optimum temperature was observed within the applied temperature range. Q10 was calculated from the linear slope in Arrhenius plots and ranged between 1.7 and 3.3 at the respective sites. The volume-specific rate (Rdark,vol) solely representing the biological temperature response was somewhat stronger, with Q10 values of 2.6 to 5.2. The Q10 values were overall not correlated to the in situ water temperature or geographical position. Accordingly, no difference in the temperature acclimation or adaptation strategy of the microbial community was observed. Slurred oxic sediment samples showed a Q10 of 1.7 and were, hence, lower than estimates based on intact sediment core measurements. This can be ascribed to changes in physical and biological controls during resuspension. Gross photosynthesis was measured with the light-dark shift method at the 2 temperate sites. Both areal (Pgross) and volumetric (Pgross,vol) rates increased with temperature to an optimum temperature at 12 and 15°C, with a Q10 for Pgross of 2.2 and 2.6 for the 2 sites, respectively. The gross photosynthesis response could be categorised as psychrotrophic for both sites and no temperature adaptation was observed between the 2 sites. Our measurements document that temperature stimulates heterotrophic activity more than gross photosynthesis, and that the benthic communities gradually become heterotrophic with increasing temperature. This has implications for C-cycling in shallow water communities experiencing seasonal and diel temperature fluctuations.

KEY WORDS: Temperature · Adaptation · Benthic microphytes · Photosynthesis · Respiration · Q10 · Microelectrodes · Oxygen

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