TEMPERATURE-DEPENDENCE OF MICROBIAL-DEGRADATION OF ORGANIC-MATTER IN MARINE-SEDIMENTS - POLYSACCHARIDE HYDROLYSIS, OXYGEN-CONSUMPTION, AND SULFATE REDUCTION

The temperature dependence of representative initial and terminal step s of organic carbon remineralization was measured at 2 temperate sites with annual temperature ranges of 0 to 30 degrees C and 4 to 15 degre es C and 2 Arctic sites with temperatures of 2.6 and -1.7 degrees C. S lurried sediments were incubated in a temperature gradient block spann ing a temperature range of ca 45 degrees C. The initial step of organi c carbon remineralization, macromolecule hydrolysis, was measured via the enzymatic hydrolysis of fluorescently labeled polysaccharides. The terminal steps of organic carbon remineralization were monitored thro ugh consumption of oxygen and reduction of (SO42-)-S-35. At each of th e 4 sites, the temperature response of the initial step of organic car bon remineralization was similar to that of the terminal steps. Althou gh optimum temperatures were always well above ambient environmental t emperatures, optimum temperatures generally decreased with decreasing environmental temperatures. Activity at 5 degrees C as a percentage of highest activity was highest in the Arctic sites and lowest in the wa rmest temperate site. The highest potential rates of substrate hydroly sis were measured in the Arctic, while the highest rates of oxygen con sumption and sulfate reduction were measured at the warmest temperate site. Potential rates of extracellular enzymatic hydrolysis (at least for this class of pullulanase enzymes) do not appear to Limit organic carbon turnover in the Arctic. These results suggest that organic carb on turnover in the cold Arctic is not intrinsically slower than carbon turnover in temperate environments; sedimentary metabolism in Arctic sediments may be controlled more by organic matter supply than by temp erature.