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

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 (R_dark,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 (P_gross) and volumetric (P_gross,vol) rates increased with temperature to an optimum temperature at 12 and 15°C, with a Q₁₀ for P_gross 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