Untersuchungen zur Produktion und zum mikrobiellen Umsatz von ß-Dimethylsulphoniopropionat
The study contains three experimental investigations; laboratory experiments about the DMSP-Produktion in cultures of marine planktonalgae, a series of field experiments about the production and turnover of particulate DMSP in the North-Sea and a series of nutrient enrichment experiments about the microbial turnover of dissolved DMSP in the tropical Atlantic. The culture experiments focused on the species-specific and the nitrogen-related variability of the DMSP-production. The observed species-specific variability of the intracellular DMSP concentration and the DMSP-production were one to two orders of magnitude higher than the range of their nitrogen-related changes and highlighted the role of key species. The importance of key species and the effect of the nutrient supply on the DMSP-production was also apparent in the series of in situ experiments in the North-Sea. About 3/4 of the total DMSP-production between March and October happened during a phase of 45 days after the vernal diatom bloom during a bloom of Phaeocystis globosa (Haptophyta) and a subsequent development of mixotrophic flagellates (cryptophyta). The maxima of the Phaeocystis bloom and of the surface concentrations of particulate DMSP coincided with a temporal minimum of the consumption of particulate DMSP by microzooplankton grazing. Apart from the Phaeocystis bloom, the consumption of particulate DMSP by microzooplankton was closely related with its production by phytoplankton and accounted on average for about 94 % of the production. About 77% of the consumed DMSP was on average released as dissolved DMSP and was in most cases microbially degraded within less than 24h. The nutrient enrichment experiments with natural size-fractionated bacteria communities in the tropical Atlantic aimed at the nutrient related variability of the DMS-yield of the decomposition of dissolved DMSP. In experiments without nutrient enrichments the DMS yield was on average 21 %. The DMS yield increased in most experiments due to organic or inorganic nutrient enrichments. The highest DMS-yields were achieved by the combined enrichments of dissolved organic sulphur and nitrogen by methionine.