No observed effect of ocean acidification on nitrogen biogeochemistry in a summer Baltic Sea plankton community
Autor: | Lennart T. Bach, Kai-Georg Schulz, Tim Boxhammer, Ulf Riebesell, Eric P. Achterberg, Mathias Haunost, Allanah J. Paul, Annegret Stuhr, Jan Czerny |
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Rok vydání: | 2015 |
Předmět: |
0106 biological sciences
010504 meteorology & atmospheric sciences lcsh:Life Biology Algal bloom 01 natural sciences Mesocosm lcsh:QH540-549.5 Phytoplankton 14. Life underwater Ecology Evolution Behavior and Systematics Earth-Surface Processes 0105 earth and related environmental sciences Ecology 010604 marine biology & hydrobiology lcsh:QE1-996.5 fungi Biogeochemistry Ocean acidification Plankton lcsh:Geology lcsh:QH501-531 Oceanography 13. Climate action lcsh:Ecology Diazotroph Bloom |
Zdroj: | Biogeosciences, Vol 13, Iss 13, Pp 3901-3913 (2016) Biogeosciences (BG), 13 . pp. 3901-3913. |
ISSN: | 1726-4189 |
Popis: | 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 neither inorganic nor organic N pool 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. |
Databáze: | OpenAIRE |
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