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High cell-specific rates of nitrogen and carbon fixation by the cyanobacterium Aphanizomenon sp at low temperatures in the Baltic Sea
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
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Number of Authors: 9
2015 (English)In: FEMS Microbiology Ecology, ISSN 0168-6496, E-ISSN 1574-6941, Vol. 91, no 12Article in journal (Refereed) Published
Abstract [en]

Aphanizomenon is a widespread genus of nitrogen (N-2)-fixing cyanobacteria in lakes and estuaries, accounting for a large fraction of the summer N-2-fixation in the Baltic Sea. However, information about its cell-specific carbon (C)- and N-2-fixation rates in the early growth season has not previously been reported. We combined various methods to study N-2-fixation, photosynthesis and respiration in field-sampled Baltic Sea Aphanizomenon sp. during early summer at 10 degrees C. Stable isotope incubations at in situ light intensities during 24 h combined with cell-specific secondary ion mass spectrometry showed an average net N-2-fixation rate of 55 fmol N cell(-1) day(-1). Dark net N-2-fixation rates over a course of 12 h were 20% of those measured in light. C-fixation, but not N-2-fixation, was inhibited by high ambient light intensities during daytime. Consequently, the C: N fixation ratio varied substantially over the diel cycle. C-and N-2-fixation rates were comparable to those reported for Aphanizomenon sp. in August at 19 degrees C, using the same methods. High respiration rates (23% of gross photosynthesis) were measured with C-14-incubations and O-2-microsensors, and presumably reflect the energy needed for high N-2-fixation rates. Hence, Aphanizomenon sp. is an important contributor to N-2-fixation at low in situ temperatures in the early growth season.

Place, publisher, year, edition, pages
2015. Vol. 91, no 12
Keyword [en]
Aphanizomenon, SIMS, isotopes, O-2-microsensors, C-fixation, N-2-fixation
National Category
Biological Sciences
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-126829DOI: 10.1093/femsec/fiv131ISI: 000368430600004OAI: oai:DiVA.org:su-126829DiVA: diva2:906473
Available from: 2016-02-24 Created: 2016-02-16 Last updated: 2016-09-14Bibliographically approved
In thesis
1. Cyanobacterial Nitrogen Fixation in the Baltic Sea: With focus on Aphanizomenon sp.
Open this publication in new window or tab >>Cyanobacterial Nitrogen Fixation in the Baltic Sea: With focus on Aphanizomenon sp.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cyanobacteria are widely distributed in marine, freshwater and terrestrial habitats. Some cyanobacterial genera can convert di-nitrogen gas (N2) to bioavailable ammonium, i.e. perform nitrogen (N) fixation, and are therefore of profound significance for N cycling. N fixation by summer blooms of cyanobacteria is one of the largest sources of new N for the Baltic Sea. This thesis investigated N fixation by cyanobacteria in the Baltic Sea and explored the fate of fixed N at different spatial and temporal scales. In Paper I, we measured cell-specific N fixation by Aphanizomenon sp. at 10 ºC, early in the season. Fixation rates were high and comparable to those in late summer, indicating that Aphanizomenon sp. is an important contributor to N fixation already in its early growth season. In Paper II, we studied fixation and release of N by Aphanizomenon sp. and found that about half of the fixed N was rapidly released and transferred to other species, including autotrophic and heterotrophic bacteria, diatoms and copepods. In Paper III, we followed the development of a cyanobacterial bloom and related changes in dissolved and particulate N pools in the upper mixed surface layer. The bloom-associated total N (TN) increase was mainly due to higher particulate organic N (PON) concentrations, but also to increases in dissolved organic nitrogen (DON). About half the PON-increase could be explained by the sum of N-fixing cyanobacteria, other phytoplankton (>2µm) and zooplankton, indicating that production was stimulated by the N fixation. In Paper IV, we used a growth model based on measured photosynthesis–irradiance relationships to explore the production potential of Aphanizomenon sp. The model included data on irradiance, biomass, temperature and light attenuation (1999–2013). Until the bloom peak, the modelled production matched the measured biomass, indicating low production losses. Over the whole season, the modelled production could explain a substantial part of the summer TN increase, assuming that plausible losses (such as grazing or cell lysis) are retained within the upper mixed layer. Complementing the other data, we also investigated the nutrient content (Paper I) and varying cell width (Paper IV) of Aphanizomenon sp. By a combination of approaches, this thesis has contributed new information on cyanobacterial N fixation rates, the transfer of fixed N to other organisms in the food web and shown the potential for fixed N to stimulate summer primary and secondary production in the Baltic Sea.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2016. 43 p.
Keyword
cyanobacteria, Baltic Sea, nitrogen fixation, Aphanizomenon sp., dissolved nitrogen, particulate nitrogen, sedimentation
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-132773 (URN)978-91-7649-481-3 (ISBN)
External cooperation:
Public defence
2016-10-14, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 215-2009-813Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 215-2010-779Max Planck SocietyBaltic Ecosystem Adaptive Management (BEAM)Swedish Research Council, 621-2011-4406Knut and Alice Wallenberg Foundation
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2016-09-21 Created: 2016-08-23 Last updated: 2016-09-12Bibliographically approved

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Svedén, Jennie B.Walve, JakobPloug, Helle
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