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Abstract

The temperature dependence of oxic mineralization processes' in perennially cold coastal sediments from Arctic Svalbard, Norway, was determined in short-term incubations at -1 to 44 degrees C and compared to similar incubations with warm temperate sediment. For oxygen respiration, nitrogen mineralization, and nitrification, adaptations to low temperature were evident with the microbial communities from Svalbard. Oxygen respiration rates showed the same temperature dependence at all sites around Svalbard, with relatively high rates at 0 degrees C and a linear 3- to 4-fold increase from 0 degrees C to a mean optimum temperature of 19.2 degrees C, whereas rates in the temperate sediment were close to zero at 0 degrees C and had optimum at 30 to 40 degrees C. The temperature dependence of nitrogen mineralization was comparable to that of oxygen respiration, and C:N mineralization ratios in the Svalbard sediments were stable at 6 to 8 below 20 degrees C. Thus, low temperature did not affect carbon and nitrogen mineralization differentially. The most prominent adaptation to low temperatures was observed for nitrification, which had a mean optimum temperature of 14.0 degrees C at Svalbard and decreased rapidly in rate at higher temperatures. In the warm temperate sediment the nitrification optimum was near 40 degrees C. The catalytic efficiency of the nitrifying communities from Svalbard, at their in situ temperature, was as high as that reported for communities from temperate regions. This implied that thermal adaptation fully compensated for direct temperature effects on this metabolism.