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| Titel |
Covariation of metabolic rates and cell size in coccolithophores |
| VerfasserIn |
G. Aloisi |
| 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 ; 12, no. 15 ; Nr. 12, no. 15 (2015-08-06), S.4665-4692 |
| Datensatznummer |
250118052
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| Publikation (Nr.) |
 copernicus.org/bg-12-4665-2015.pdf |
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| Zusammenfassung |
| Coccolithophores are sensitive recorders of environmental change. The size
of their coccosphere varies in the ocean along gradients of environmental
conditions and provides a key for understanding the fate of this important
phytoplankton group in the future ocean. But interpreting field changes in
coccosphere size in terms of laboratory observations is hard, mainly because
the marine signal reflects the response of multiple morphotypes to changes
in a combination of environmental variables. In this paper I examine the
large corpus of published laboratory experiments with coccolithophores
looking for relations between environmental conditions, metabolic rates and
cell size (a proxy for coccosphere size). I show that growth,
photosynthesis and, to a lesser extent, calcification covary with cell size
when pCO2, irradiance, temperature, nitrate, phosphate and iron
conditions change. With the exception of phosphate and temperature, a change
from limiting to non-limiting conditions always results in an increase in
cell size. An increase in phosphate or temperature (below the optimum
temperature for growth) produces the opposite effect. The magnitude of the
coccosphere-size changes observed in the laboratory is comparable to that
observed in the ocean. If the biological reasons behind the
environment–metabolism–size link are understood, it will be possible to use
coccosphere-size changes in the modern ocean and in marine sediments to
investigate the fate of coccolithophores in the future ocean. This reasoning
can be extended to the size of coccoliths if, as recent experiments are
starting to show, coccolith size reacts to environmental change
proportionally to coccosphere size. The coccolithophore database is strongly
biased in favour of experiments with the coccolithophore Emiliania huxleyi (E. huxleyi; 82 % of
database entries), and more experiments with other species are needed to
understand whether these observations can be extended to coccolithophores in
general. I introduce a simple model that simulates the growth rate and the
size of cells forced by nitrate and phosphate concentrations. By considering
a simple rule that allocates the energy flow from nutrient acquisition to
cell structure (biomass) and cell maturity (biological complexity,
eventually leading to cell division), the model is able to reproduce the
covariation of growth rate and cell size observed in laboratory experiments
with E. huxleyi when these nutrients become limiting. These results support ongoing
efforts to interpret coccosphere and coccolith size measurements in the
context of climate change. |
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