 |
| Titel |
Size-fractionated dissolved primary production and carbohydrate composition of the coccolithophore Emiliania huxleyi |
| VerfasserIn |
C. Borchard, A. Engel |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 4 ; Nr. 12, no. 4 (2015-02-27), S.1271-1284 |
| Datensatznummer |
250117836
|
| Publikation (Nr.) |
 copernicus.org/bg-12-1271-2015.pdf |
|
|
|
|
|
| Zusammenfassung |
| Extracellular release (ER) by phytoplankton is the major source of fresh
dissolved organic carbon (DOC) in marine ecosystems and accompanies primary
production during all growth phases. Little is known, so far, on size and
composition of released molecules, and to which extent ER occurs passively,
by leakage, or actively, by exudation. Here, we report on ER by the
widespread and bloom-forming coccolithophore Emiliania huxleyi grown
under steady-state conditions in phosphorus-controlled chemostats
(N:P = 29, growth rate of μ = 0.2 d−1) at present-day
and high-CO2 concentrations. 14C incubations were performed to
determine primary production (PP), comprised of particulate (PO14C) and
dissolved organic carbon (DO14C). Concentration and composition of
particulate combined carbohydrates (pCCHO) and high-molecular-weight
(>1 kDa, HMW) dissolved combined carbohydrates (dCCHO) were determined
by ion chromatography. Information on size distribution of ER products was
obtained by investigating distinct size classes (<0.4 μm
(DO14C), <0.45 μm (HMW-dCCHO), <1000, <100 and
<10 kDa) of DO14CC and HMW-dCCHO. Our results revealed relatively
low ER during steady-state growth, corresponding to ~4.5% of
primary production, and similar ER rates for all size classes. Acidic sugars
had a significant share on freshly produced pCCHO as well as on
HMW-dCCHO. While pCCHO and the smallest size fraction (<10 kDa) of
HMW-dCCHO exhibited a similar sugar composition, dominated by high
percentage of glucose (74–80 mol%), the composition of HMW-dCCHO
size classes >10 kDa was significantly different, with a higher
mol% of arabinose. The mol% of acidic sugars increased and that of
glucose decreased with increasing size of HMW-dCCHO. We conclude that
larger polysaccharides follow different production and release pathways than
smaller molecules, potentially serving distinct ecological and biogeochemical
functions. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|