Measurement of depth- and site-related differences in polysaccharide hydrolysis rates in marine sediments

Abstract

The rates at which organic macromolecules are remineralized, and variations in degradation rates with site and depth, are critical aspects in calculating the turnover of oceanic organic carbon. This work introduces a new approach to measuring extracellular enzymatic hydrolysis rates in seawater and sediments, and reports first results from field measurements. The technique, based on measurements with fluorescently labeled polysaccharides (FLA-polysaccharides), was used to measure potential hydrolysis rates of pullulan in sediments at three different sites (mud, sand, sandy mud) in Kiel Bight, Baltic Sea. Significant depth- and site-related differences were measured for the enzymatic hydrolysis of FLA-pullulan. The total range of hydrolysis rates for FLA-pullulan (3–109 cuts · nmol glu · cm −3 · h −1) was considerably higher than rates previously reported for MUF-β-glucose in Kiel Bight sediments. The highest rates were measured in mud samples at depths of 0–2 cm and in black banded sands at depths of 5–10 cm, while the lowest rates were measured at depths of 8–12 cm in sandy mud samples. The results obtained with the new method confirm that at least some types of polysaccharides are rapidly hydrolyzed in marine sediments.