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| Titel |
Organic matter exudation by Emiliania huxleyi under simulated future ocean conditions |
| VerfasserIn |
C. Borchard, A. Engel |
| 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 ; 9, no. 8 ; Nr. 9, no. 8 (2012-08-27), S.3405-3423 |
| Datensatznummer |
250007254
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| Publikation (Nr.) |
 copernicus.org/bg-9-3405-2012.pdf |
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| Zusammenfassung |
Emiliania huxleyi (strain B 92/11) was exposed to different nutrient supply, CO2 and
temperature conditions in phosphorus controlled chemostats to investigate
effects on organic carbon exudation and partitioning between the pools of
particulate organic carbon (POC) and dissolved organic carbon (DOC).
14C incubation measurements for primary production (PP) and
extracellular release (ER) were performed. Chemical analysis included the amount
and composition of high molecular weight (>1 kDa) dissolved combined
carbohydrates (HMW-dCCHO), particulate combined carbohydrates (pCCHO) and
the carbon content of transparent exopolymer particles (TEP-C). Applied
CO2 and temperature conditions were 300, 550 and 900 μatm
pCO2 at 14 °C, and additionally 900 μatm pCO2 at 18 °C
simulating a greenhouse ocean scenario.
Enhanced nutrient stress by reducing the dilution rate (D) from D = 0.3 d−1
to D = 0.1 d−1 (D = μ) induced the strongest response in E. huxleyi. At μ = 0.3 d−1, PP
was significantly higher at elevated CO2 and temperature and DO14C
production correlated to PO14C production in all treatments, resulting
in similar percentages of extracellular release (PER; (DO14C
production/PP) × 100) averaging 3.74 ± 0.94%. At μ = 0.1 d−1,
PO14C production decreased significantly, while exudation of DO14C
increased. Thus, indicating a stronger partitioning from the particulate to
the dissolved pool. Maximum PER of 16.3 ± 2.3% were observed at μ = 0.1 d−1
at elevated CO2 and temperature.
While cell densities remained constant within each treatment and throughout
the experiment, concentrations of HMW-dCCHO, pCCHO and TEP were generally
higher under enhanced nutrient stress. At μ = 0.3 d−1, pCCHO
concentration increased significantly with elevated CO2 and
temperature. At μ = 0.1 d−1, the contribution (mol % C) of HMW-dCCHO to
DOC was lower at elevated CO2 and temperature while pCCHO and TEP
concentrations were higher. This was most pronounced under greenhouse
conditions. Our findings suggest a stronger transformation of primary
produced DOC into POC by coagulation of exudates under nutrient limitation.
Our results further imply that elevated CO2 and temperature will
increase exudation by E. huxleyi and may affect organic carbon partitioning in the
ocean due to an enhanced transfer of HMW-dCCHO to TEP by aggregation
processes. |
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