engleski

Effects of nutrient addition on microbial plankton and dissolved organic matter variability. Part 2: biochemical aspect.

Growing in microcosms of natural planktonic popilations stimulated by the addition of nutrients was followed for organic matter production and excretion. Addition of phosphate or a mixture of nutrients (P, N, Si) enhanced the primary production, and increased the biomass. This was recorded in terms of chlorophyll and also particulate organic carbon (POC) which doubled in a few days. In a first experiment (PALEX 1, June 1994), not any dissolved organic carbon (DOC) accumulation could be evidenced. In a second one (PALEX 2, April 1995), a large increase in DOC was observed. The DOC content increased by a factor two, due to an important production of polysaccharides. This increase in polysaccharides concentration started on the second day of experiment, exhibiting higher rate than the total DOC increase. This result suggests that a fraction of the initial dissolved organic matter, probably proteic in nature, was rapidly consumed during the first 2-3 days when bacterial production was increasing. The excretion of polysaccharides is rapidly followed by a change in pigments concentration, chlorophyll a decreasing while chlorophyllids are increasing. This was interpreted as the mark that the planktonic population was in a senescent phase. The experiment puts in evidence one of the mechanisms responsible of DOC accumulation that can be at the origin of the formation of large aggregates and the accumulation of mucilagionous structure frequently observed in Northern Adriatic.

Adriatic; microbial plankton; dissolved organic matter

nije evidentirano