http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0079890
Iron Limitation Modulates Ocean Acidification Effects on Southern Ocean
Phytoplankton Communities
- Clara J. M. Hoppe,
- Christel S. Hassler,
- Christopher D. Payne,
- Philippe D. Tortell,
- Björn Rost,
- Scarlett Trimborn
- Published: Nov 20, 2013
- DOI: 10.1371/journal.pone.0079890
Abstract
The potential interactive effects of iron (Fe) limitation and Ocean
Acidification in the Southern Ocean (SO) are largely unknown. Here we
present results of a long-term incubation experiment investigating the
combined effects of CO2 and Fe availability on natural phytoplankton
assemblages from the Weddell Sea, Antarctica. Active Chl *a* fluorescence
measurements revealed that we successfully cultured phytoplankton under
both Fe-depleted and Fe-enriched conditions. Fe treatments had significant
effects on photosynthetic efficiency (Fv/Fm; 0.3 for Fe-depleted and 0.5
for Fe-enriched conditions), non-photochemical quenching (NPQ), and
relative electron transport rates (rETR). pCO2 treatments significantly
affected NPQ and rETR, but had no effect on Fv/Fm. Under Fe limitation,
increased pCO2 had no influence on C fixation whereas under Fe enrichment,
primary production increased with increasing pCO2 levels. These CO2-dependent
changes in productivity under Fe-enriched conditions were accompanied by a
pronounced taxonomic shift from weakly to heavily silicified diatoms (i.e.
from *Pseudo-nitzschia* sp. to *Fragilariopsis* sp.). Under Fe-depleted
conditions, this functional shift was absent and thinly silicified species
dominated all pCO2 treatments (*Pseudo-nitzschia* sp. and*Synedropsis* sp.
for low and high pCO2, respectively). Our results suggest that Ocean
Acidification could increase primary productivity and the abundance of
heavily silicified, fast sinking diatoms in Fe-enriched areas, both
potentially leading to a stimulation of the biological pump. Over much of
the SO, however, Fe limitation could restrict this possible CO2 fertilization
effect."
regards
Bhaskar
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