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| Titel |
Primary production during nutrient-induced blooms at elevated CO2 concentrations |
| VerfasserIn |
J. K. Egge, T. F. Thingstad, A. Larsen, A. Engel, J. Wohlers, R. G. J. Bellerby, U. Riebesell |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 6, no. 5 ; Nr. 6, no. 5 (2009-05-20), S.877-885 |
| Datensatznummer |
250003749
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| Publikation (Nr.) |
 copernicus.org/bg-6-877-2009.pdf |
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| Zusammenfassung |
| A CO2 enrichment experiment (PeECE III) was carried out in 9 mesocosms
in which the seawater carbonate system was manipulated to achieve three
different levels of pCO2. At the onset of the experimental period,
nutrients were added to all mesocosms in order to initiate phytoplankton
blooms. Primary production rates were measured by in-vitro incubations based
on 14C-incorporation and oxygen production/consumption. Size
fractionated particulate primary production was also determined by 14C
incubation and is discussed in relation to phytoplankton composition.
Primary production rates increased in response to nutrient addition and a
net autotrophic phase with 14C-fixation rates up to 4 times higher than
initial was observed midway through the 24 days experiment before net
community production (NCP) returned to near-zero and 14C-fixation rates
dropped below initial values. No clear heterotrophic phase was observed
during the experiment. Based on the 14C-measurements we found higher
cumulative primary production at higher pCO2 towards the end of the
experiment. CO2 related differences were also found in size
fractionated primary production. The most noticeable responses to CO2
treatments with respect to primary production rates occurred in the second
half of the experiment when phytoplankton growth had become nutrient
limited, and the phytoplankton community changed from diatom to flagellate
dominance. This opens for two alternative hypotheses that the effects are
either associated with mineral nutrient limited growth, and/or with a change
in phytoplankton species composition. The lack of a clear net heterotrophic
phase in the last part of the experiment supports the idea that a
substantial part of production in the upper layer was not degraded locally,
but either accumulated or exported vertically. |
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