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

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) O 2 exchange were determined from O 2 -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 O 2 consumption increased exponentially with increasing temperature for both TOE and DOE, and no optimum temperature was observed within the applied temperature range. Q 10 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 Q 10 values of 2.6 to 5.2. The Q 10 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 Q 10 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 Q 10 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.

Benthic primary productivity on the Georgia midcontinental shelf: Benthic flux measurements and high‐resolution, continuous in situ PAR records

“…The temperature range observed here (14 -28°C) is modest (Table 1) and a temperature effect on BPP is obscured by the dominant response to variability in PAR flux. The absence of strong temperature dependence in our regression analysis is consistent with the results of Hancke and Glud [2004] for temperate and arctic benthic photosynthesis and Behrenfeld and Falkowski [1997] for planktonic autotrophs. Both studies observed a broad maximum in photosynthetic response with respect to temperature, with a decrease in response at the highest temperatures surveyed.…”

Primary Production in the Ocean

“…The microphytobenthos is usually limited to the surface 2 or 3 mm of sediment, therefore high resolution measurements are required; photosynthesis is measured to a resolution of 100 m and the sensing tips of the microelectrode have diameters of only 2 -10 m (Revsbech et al, 1989). While oxygen microelectrodes just measure oxygen concentration, it is possible to measure gross photosynthesis rates using the light-dark shift method (Revsbech & Jørgensen, 1983;Glud et al, 1992;Lassen et al, 1998;Hancke & Glud, 2004). Moreover, oxygen concentration profiles can be used to calculate respiration and net photosynthesis rates according to Kühl et al (1996) and Hancke & Glud (2004) based on Fick's first law of diffusion.…”

“…While oxygen microelectrodes just measure oxygen concentration, it is possible to measure gross photosynthesis rates using the light-dark shift method (Revsbech & Jørgensen, 1983;Glud et al, 1992;Lassen et al, 1998;Hancke & Glud, 2004). Moreover, oxygen concentration profiles can be used to calculate respiration and net photosynthesis rates according to Kühl et al (1996) and Hancke & Glud (2004) based on Fick's first law of diffusion. Estimates of benthic primary productivity are also made using oxygen exchange across the sediment-water interface using benthic chambers or sediment cores (Thornton et al, 2002).…”

Benthic fluxes of oxygen and nutrients in sublittoral fine sands in a north-western Mediterranean coastal area

“…In this study, we have observed that benthic respiration could be driven by quantitative changes in labile fraction of sedimentary organics throughout the year. However, Ní Longphuirt et al (2007) and Ferrón et al (2009a) observed in other coastal areas that benthic respiration was not related to temperature or total organic matter, notwithstanding changes in both these variables could induce alterations in heterotrophic processes (Hancke and Glud, 2004).…”