Phytoplankton Exudates Research Articles

Phytoplankton exudate release as an energy source for the growth of pelagic bacteria

The release of dissolved organic carbon (DOC) from phytolankton during photosynthesis, and the utilization of this carbon by planktonic bacteria, was studied using 14CO2 and selective filtration. Natural sea water samples from a coastal area of the Northern Baltic Sea were incubated in the laboratory for detailed studies, and in situ for estimation of annual dynamics. In a laboratory incubation (at +1°C) the concentration of 14C-labelled dissolved organic carbon increased for about 2 h and then reached a steady state, representing about 0. 1% of the total DOC. Labelled organic carbon in the phytoplankton and bacterial fractions continued to increase almost linearly. The continuous increase in the bacterial fraction is thought to represent almost instantaneous utilization of the DOC released from the phytoplankton during photosynthesis. As an annual average, in 4 h in situ incubations, about 65% of the labelled organic carbon was found in the phytoplankton fraction (>3 μm), about 27% in the bacterial fraction (0.2 to 3 μm) and the remaining 8% as DOC (<0.2 μm). Large variations in these percentages were recorded. The measured annual primary production was 93 g C m-2 (March to December), and the estimated bacterial production due to phytoplankton exudates 29 g C m-2. This represents a release of DOC of about 45% of the corrected annual primary production of 110 g C m-2 (assuming a bacterial growth efficiency of 0.6).

Phytoplankton exudate release as an energy source for the growth of pelagic bacteria : Larsson, U. and A. Hagstrom, 1979. Mar. Biol., 52(3): 199–206

Phytoplankton exudate release as an energy source for the growth of pelagic bacteria : Larsson, U. and A. Hagstrom, 1979. Mar. Biol., 52(3): 199–206

Potentiometric determination of copper complexation by phytoplankton exudates 1

Potentiometric copper titrations were done on culture media in which eight algal species, Thalassiosira pseudonana (3H), Ankistrodesmus falcatus, Chlamydomonas sp., Pediastrum sp., Staurastrum gracile, Gloeocystis gigas, Tribonema sp., and Cyclotella cryptica were grown to cell concentrations of 105–106 cells · ml−1. The results demonstrate that only G. gigas produces extracellular organic compounds that can measurably reduce the cupric ion activity in 1 × 10−6 M total copper.

Observations of heterotrophic activity on photoassimilated organic matter

The natural heterotrophic utilization of released and particulate photoassimilated compounds by natural phytoplankton populations was followed during the summer of 1975 in the Kiel Bight (Western Baltic Sea). Phytoplankton exudates (2 to 21% of primary production) seem to represent an important substrate for heterotrophic bacteria: uptake rates between 8 and 17,5%/h were observed. Samples incubated with antibiotics indicated that the heterotrophic uptake of phytoplankton exudates during photosynthesis could lead to underestimation of the release rate. Production of 14CO 2was used as an estimate of the mineralization of particulate photoassimilated matter. The mineralization rates measured were in the range of 6 to 20% after 20 h. In order to confirm the quantitative measurements, micro-autoradiographic examinations of the samples were performed.

High molecular weight algal substances in the sea

Phytoplankton exudates into culture media and extracts from littoral algae are shown to contain significant quantities of extracellular materials having molecular weights in excess of 50,000. A recent development in experimental fluid mechanics (the reduction of turbulent friction coefficients of flowing solutions by dissolved macromolecules) has been utilized as a specific test for high molecular weight compounds. Phytoplankton species in all major algal groups could be found which exude high molecular weight compounds into their culture media; the red alga Porphyridium cruentum typically produced friction reductions as high as 60%. Seaweed samples in the Chlorophyta, Phaeophyta, and Rhodophyta showed major changes in turbulent friction coefficient; in some cases the friction was less than 1/2 that of pure seawater. All samples of the genus Porphyra and Gigartina produced substantial friction changes. From these experiments it is concluded that algal exudates can be a prominent source of high molecular weight compounds in the sea.