Photosynthetic carbon metabolism and biochemical composition of spring phytoplankton assemblages enclosed in microcosms: the diatom-Phaeocystis sp. Succession
Year: 1992
Type: article
Abstract: Samples of natural phytoplankton assemblages were taken on 4 occasions between 28 March and 19 April 1990 at 2 stations located to the southwest of Plymouth (UK) and incubated in experimental microcosms under constant light and temperature.14C incorporation into cell constituents [proteins, polysaccharides, lipids and low molecular weight metabolites (LMWM)] and the biochemical compos~tion of the phytoplankton were monitored during the experiments.Different phytoplankton populations developed in the microcosms.Microflagellates which dominated in the f~rst experiments were followed in later experiments by a multispecific bloom of chain-forming diatoms, and these in turn by a bloom of Phaeocystis sp.Each assemblage was characterized by a different metabolic behaviour High '"C incorporation into LMWM and lip~ds was observed during non-growth periods when microflagellates dominated.High '"C incorporation into proteins and relatively high specific rates of protein synthesis (0.45 f 0.1 d-l) were measured during the late growth phase of the diatom bloom.Synthesis of acid-soluble carbohydrates (ASC) also occurred in this period.As Phaeocystis sp.increased.I4C incorporation into LMWM and polysaccharides showed a significant rise.These metabolic patterns were consistent with earlier models of the development of Phaeocystis sp.blooms.Polysaccharidecarbon concentration, both acid-soluble and acid-insoluble, showed dramatic increases during the early stages of the bloom.Enhanced polysaccharide synthesis was related to the formation of the mucilaginous colonial matrix and is suggested to be a physiological strategy tending to increase colony buoyancy.During the decline of the Phaeocystjs sp.bloom, the proportion of 14C incorporated into LMWM decreased, possibly as a result of disruption of the colonies, whereas incorporation into lipids exhibited a consistent increase.The accumulation of high-energy storage products is interpreted as a metabolic adaptation for overwintering under very low light levels.As a consequence of the distinct metabolic patterns of each successional stage, the protein-C/acid-insoluble polysaccharide-C ratio showed a marked decrease, whereas the relative contribution of ASC-C to the total measured carbon displayed a significant increase.In addition, carbon incorporation into LMWM also showed a slight but continuous increase.It is suggested that the metabolic changes associated with the diatom -Phaeocystis sp.succession are in accord with a marked shift in the trophic structure of the planktonic ecosystem from the classical food chain in the earlier stages, and mainly during the diatom bloom, to a preponderance of the microbial loop at the end of the Phaeocystis sp.bloom
Source: Marine Ecology Progress Series
DOI: 10.3354/meps090089
Language: English
Subfield: Oceanography
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2087112781