ABSTRACT: Short-term temperature effects on oxygen turn-over in artificial cold-adapted microbial mats were experimentally studied using microsensor techniques. The artificial mats were cultured in benthic gradient chambers under opposing oxygen and sulphide gradients, and community metabolism was analysed after 8 mo of incubation at 5°C. Microbial mat samples from Lake Fryxell (Antarctica) were used as inocula. Both net and gross O₂ productivity were maximal at 10°C, whereas gross O₂ production was completely inhibited at 15°C. Thus, the microbial community exhibited a psychrophilic response. Nevertheless, the inhibition of oxygenic photosynthesis at 15°C might result from indirect effects of accumulation of H₂S in the photic zone, which might induce the inhibition of photosystem II activity. The dynamics of the dark and light net metabolism of O₂ were estimated from transient oxygen profiles. They were strongly affected by the temperature changes, exhibiting temperature characteristics well above those calculated from the steady-state approaches. This indicates that indirect effects of temperature probably occurred, i.e. (1) migration of microorganisms locally resulting in higher biomass, (2) an increase of the oxygen requirements for the oxidation of reduced compounds such as H₂S, or both. The results show that the metabolic rates of the different functional groups in these artificial microbial mats were fine-tuned to the prevailing temperature. This resulted in a close coupling of oxygen and sulphur cycles as has been previously found for mesophilic hypersaline mats.

KEY WORDS: Microsensors · Photosynthesis · Respiration · Psychrophilic community · Lake Fryxell

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Published in AME Vol. 26, No. 2 (2001) on December 5
Print ISSN: 0948-3055; Online ISSN: 1616-1564. Copyright © Inter-Research, Oldendorf/Luhe, 2001