The impact of temperature change on the activity and community composition of sulfate‐reducing bacteria in arctic versus temperate marine sediments

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Abstract
P>Arctic regions may be particularly sensitive to climate warming and, consequently, rates of carbon mineralization in warming marine sediment may also be affected. Using long-term (24 months) incubation experiments at 0 degrees C, 10 degrees C and 20 degrees C, the temperature response of metabolic activity and community composition of sulfate-reducing bacteria were studied in the permanently cold sediment of north-western Svalbard (Arctic Ocean) and compared with a temperate habitat with seasonally varying temperature (German Bight, North Sea). Short-term S-35-sulfate tracer incubations in a temperature-gradient block (between -3.5 degrees C and +40 degrees C) were used to assess variations in sulfate reduction rates during the course of the experiment. Warming of arctic sediment resulted in a gradual increase of the temperature optima (T-opt) for sulfate reduction suggesting a positive selection of psychrotolerant/mesophilic sulfate-reducing bacteria (SRB). However, high rates at in situ temperatures compared with maximum rates showed the predominance of psychrophilic SRB even at high incubation temperatures. Changing apparent activation energies (E-a) showed that increasing temperatures had an initial negative impact on sulfate reduction that was weaker after prolonged incubations, which could imply an acclimatization response rather than a selection process of the SRB community. The microbial community composition was analysed by targeting the 16S ribosomal RNA using catalysed reporter deposition fluorescence in situ hybridization (CARD-FISH). The results showed the decline of specific groups of SRB and confirmed a strong impact of increasing temperatures on the microbial community composition of arctic sediment. Conversely, in seasonally changing sediment sulfate reduction rates and sulfate-reducing bacterial abundance changed little in response to changing temperature.