No observed effect of ocean acidification on nitrogen biogeochemistry in a summer Baltic Sea plankton community.

Paul, Allanah J., Achterberg, Eric P. , Bach, Lennart T. , Boxhammer, Tim , Czerny, Jan, Haunost, Mathias, Schulz, Kai G., Stuhr, Annegret and Riebesell, Ulf (2016) No observed effect of ocean acidification on nitrogen biogeochemistry in a summer Baltic Sea plankton community. Open Access Biogeosciences (BG), 13 . pp. 3901-3913. DOI 10.5194/bg-13-3901-2016.

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Abstract

Nitrogen fixation by filamentous cyanobacteria supplies significant amounts of new nitrogen (N) to the Baltic Sea. This balances N loss processes such as denitrification and anammox and forms an important N source supporting primary and secondary production in N-limited post-spring bloom plankton communities. Laboratory studies suggest that filamentous diazotrophic cyanobacteria growth and N2-fixation rates are sensitive to ocean acidification with potential implications for new N supply to the Baltic Sea. In this study, our aim was to assess the effect of ocean acidification on diazotroph growth and activity as well as the contribution of diazotrophically-fixed N to N supply in a natural plankton assemblage. We enclosed a natural plankton community in a summer season in the Baltic Sea near the entrance to the Gulf of Finland in six large-scale mesocosms (volume ~ 55 m3) and manipulated fCO2 over a range relevant for projected ocean acidification by the end of this century (average treatment fCO2: 365–1231 μatm). The direct response of diazotroph growth and activity was followed in the mesocosms over a 47 day study period during N-limited growth in the summer plankton community. Diazotrophic filamentous cyanobacteria abundance throughout the study period and N2-fixation rates (determined only until day 21 due to subsequent use of contaminated commercial 15N-N2 gas stocks) remained low. Thus estimated new N inputs from diazotrophy were too low to relieve N limitation and stimulate a summer phytoplankton bloom. Instead regeneration of organic N sources likely sustained growth in the plankton community. We could not detect significant CO2-related differences in inorganic or organic N pools sizes, or particulate matter N : P stoichiometry. Additionally, no significant effect of elevated CO2 on diazotroph activity was observed. Therefore, ocean acidification had no observable impact on N cycling or biogeochemistry in this N-limited, post-spring bloom plankton assemblage in the Baltic Sea.

Document Type: Article
Funder compliance: info:eu-repo/grantAgreement/EC/FP7/228224
Keywords: ocean acidification, nitrogen biogeochemistry, plankton, summer, Baltic Sea
Research affiliation: OceanRep > The Future Ocean - Cluster of Excellence > FO-R07
OceanRep > The Future Ocean - Cluster of Excellence > FO-R05
OceanRep > The Future Ocean - Cluster of Excellence > FO-R08
OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
Kiel University
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.5194/bg-13-3901-2016
ISSN: 1726-4170
Projects: KOSMOS, Future Ocean, BIOACID, SOPRAN, MESOAQUA
Expeditions/Models/Experiments:
Date Deposited: 30 Oct 2015 13:19
Last Modified: 23 Sep 2019 18:23
URI: http://oceanrep.geomar.de/id/eprint/30124

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