| 1. |
- Andersson, Agneta, et al.
(författare)
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Release of aminoacids and inorganic nutrients by heterotrophic marine microflagellates
- 1985
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Ingår i: Marine Ecology Progress Series. - 0171-8630 .- 1616-1599. ; 23, s. 99-106
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Tidskriftsartikel (refereegranskat)abstract
- Heterotrophic microflagellates isolated from the Baltic Sea and grown under laboratoryconditions were shown to release dissolved free amino acids (DFAA) when grazing bacteria. Flagellatesreleased 3H-amino acids when fed 3H-leucine-labelled bacteria, and concentrations of aminoacids increased in the experimental medium. Serine showed a strong positive correlation withflagellate feeding. Aspartic acid, glutamic acid and ornithine also increased more than other aminoacids. During consumption of bacteria, the flagellates released 13% of the ingested nitrogen asammonia, and 30 % of the ingested phosphorus as phosphate. In a field experiment off Scripps Pier, wemeasured bacterial production, flagellate abundance, and concentration of DFAA over a 28 h period.The concentration of DFAA showed a covariation with the flagellate numbers. Results from our fieldand laboratory experiments suggest that flagellates may be a source of DFAA in the sea.
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| 2. |
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| 3. |
- Fuhrman, J.A., et al.
(författare)
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Diel variations in bacterioplankton, phytoplankton, and related parameters in the Southern California Bight.
- 1985
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Ingår i: Marine Ecology Progress Series. - 0171-8630 .- 1616-1599. ; 27, s. 9-20
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Tidskriftsartikel (refereegranskat)abstract
- The principal objectives of this study were (i) to determine the extent of coupling betweenphytoplankton and microheterotrophs on the shelf off Southern California. (ii) to compare differentmeasures of primary and bacterial secondary production, and (iii) to assess whether sampling timesshould be as strictly controlled for microheterotroph as for autotroph studies. Two diel cycles (May andOctober) were studied by sampling an isotherm as the ship followed paired submerged drogues. Wefound significant die1 changes of chlorophyll, 14C bicarbonate incorporation, bacterial abundance andthymidine incorporation, frequency of dividing bacterial cells (FDC), abundance of non-pigmentedflagellates, particulate organic carbon and nitrogen and their ratios, and dissolved oxygen. Theseparameters all had higher values dunng daylight hours than at night, showing close coupling betweenthe phytoplankton (light-forced) and the microheterotrophs. The ratio of in vivo to extractedchlorophyll a fluorescence, however, displayed a maximum at midnight and minimum at midday,suggesting an endogenous rhythm. Primary production measured by the 14C method was similar to netproduction inferred from in situ oxygen changes. Short-lived peaks in FDC values suggested partlysynchronized bacterial division.
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| 4. |
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| 5. |
- Hagström, Åke, et al.
(författare)
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Microbial loop in an oligotrophic pelagic marine ecosystem: Possible roles of cyanobacteria and nanoflagellates in the organic fluxes
- 1988
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Ingår i: Marine Ecology Progress Series. - 0171-8630 .- 1616-1599. ; 49, s. 171-178
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Tidskriftsartikel (refereegranskat)abstract
- In an attempt to quantify the organic fluxes within the microbial loop of oligotrophicMediterranean water, organic pools and production rates were monitored. The production of cyanobacteriaand its dynamics dominated the overall productivity in the system. The largest standing stock wasthat of the bacterioplankton and its growth consumed 8.3 pg C 1-' d-', hence about 60 % of the primaryproduction was required for bacterial growth. Using the MiniCap technique, we measured a predationon bacteria of 2 6 X 104 bacteria ml-' h-'. This was in good agreement with the bacterial production rateof 2.3 X 104 cells rnl-' h-' Thus, growth and predation were balanced for heterotrophic bacterioplankton.Almost all of this predation on bacteria was due to organisms passing a 12 vm Nuclepore filter. Thisraises the question of what mechanisms channel 60 % of primary production into bacteria. We thereforeoutlined a mass-balance model to illustrate routes that could explain this transfer. According to ourmodel the main flux route is cyanobacteria and concomitantly consumed heterotrophic bacteria carboninto bacterivores. A substantial fraction of the bacterivore and the microplankton carbon is released byexcretion and/or cell lysis, to be used by the heterotrophic bacterioplankton. About 86% of theautotrophic production is balanced by respiration due to heterotrophic bacteria and protozoa, leaving6 % of the primary production to higher trophic levels. This scenario should apply to ecosystems wherebacterial production rate is high and comparable to primary production, and the dominant primaryproducers are cyanobacteria. A significant fraction of the photosynthetically fixed carbon will bemineralized within a simple microbial loop, thus rendering it an energy sink in the foodweb.
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| 6. |
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| 7. |
- Horrigan, S.G., et al.
(författare)
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Inorganic nitrogen utilization by assemblages of marine bacteria in seawater culture
- 1988
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Ingår i: Marine Ecology Progress Series. - 0171-8630 .- 1616-1599. ; 50, s. 147-150
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Tidskriftsartikel (refereegranskat)abstract
- Stimulation of heterotrophic bacterial growth by inorganic nitrogen (nitrate and ammonium) was observed in natural assemblages of marine bacteria growth in continuous culture with unsupplemented sea water as primary medium. In the presence of nitrogenous supplements, bacterial numbers increased approximately 3-fold. These results indicate that re-evaluation of the role of heterotrophic bacterioplankton in the pelagic nitrogen cycle may be necessary.
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| 8. |
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| 9. |
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| 10. |
- Wikner, Johan, 1961-, et al.
(författare)
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Evidence for a tightly coupled nanoplanktonic predator-prey link regulating the bacterivores in the marine-environment
- 1988
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Ingår i: Marine Ecology Progress Series. - Oldenburg : Inter-Research. - 0171-8630 .- 1616-1599. ; 50:1-2, s. 137-145
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Tidskriftsartikel (refereegranskat)abstract
- A coupled predator-prey chain, starting with bactenvores, was invest~gated using the mlnicell recapture technique (MiniCap) Water samples were subjected to slze fract~onation wth decreasing filter pore sue in order to obtain a successive truncation of the microbial food chaln Our results showed that the malor bacterivores were flagellates in the size range of 1 to 3 pm The truncation of the food chain caused increased or decreased predation on the bactena, d e p e n d~n go n whether the bacterivores 'ivere released from or subjected to increased predat~on pressure We present a model describing trophic interactions between organisms less than 12 pm In size This model suggests 4 trophic levels to form a regulatory chain exer t~nga tight control on major bacterivores.
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