Change search
ReferencesLink to record
Permanent link

Direct link
Cyanobacterial Nitrogen Fixation in the Baltic Sea: With focus on Aphanizomenon sp.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
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 [en]
cyanobacteria, Baltic Sea, nitrogen fixation, Aphanizomenon sp., dissolved nitrogen, particulate nitrogen, sedimentation
National Category
Ecology
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-132773ISBN: 978-91-7649-481-3OAI: oai:DiVA.org:su-132773DiVA: diva2:954987
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
List of papers
1. High cell-specific rates of nitrogen and carbon fixation by the cyanobacterium Aphanizomenon sp at low temperatures in the Baltic Sea
Open this publication in new window or tab >>High cell-specific rates of nitrogen and carbon fixation by the cyanobacterium Aphanizomenon sp at low temperatures in the Baltic Sea
Show others...
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.

Keyword
Aphanizomenon, SIMS, isotopes, O-2-microsensors, C-fixation, N-2-fixation
National Category
Biological Sciences
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-126829 (URN)10.1093/femsec/fiv131 (DOI)000368430600004 ()
External cooperation:
Available from: 2016-02-24 Created: 2016-02-16 Last updated: 2016-09-14Bibliographically approved
2. N2-fixation, ammonium release and N-transfer to the microbial and classical food web within a plankton community
Open this publication in new window or tab >>N2-fixation, ammonium release and N-transfer to the microbial and classical food web within a plankton community
Show others...
2016 (English)In: The ISME Journal, ISSN 1751-7362, E-ISSN 1751-7370, Vol. 10, no 2, 450-459 p.Article in journal (Refereed) Published
Abstract [en]

We investigated the role of N2-fixation by the colony-forming cyanobacterium, Aphanizomenon spp., for the plankton community and N-budget of the N-limited Baltic Sea during summer by using stable isotope tracers combined with novel secondary ion mass spectrometry, conventional mass spectrometry and nutrient analysis. When incubated with 15N2Aphanizomenon spp. showed a strong 15N-enrichment implying substantial 15N2-fixation. Intriguingly, Aphanizomenon did not assimilate tracers of 15NH4+ from the surrounding water. These findings are in line with model calculations that confirmed a negligible N-source by diffusion-limited NH4+ fluxes to Aphanizomenon colonies at low bulk concentrations (<250 nm) as compared with N2-fixation within colonies. No N2-fixation was detected in autotrophic microorganisms <5 μm, which relied on NH4+uptake from the surrounding water. Aphanizomenon released about 50% of its newly fixed N2 as NH4+. However, NH4+ did not accumulate in the water but was transferred to heterotrophic and autotrophic microorganisms as well as to diatoms (Chaetoceros sp.) and copepods with a turnover time of ~5 h. We provide direct quantitative evidence that colony-formingAphanizomenon releases about half of its recently fixed N2 as NH4+, which is transferred to the prokaryotic and eukaryotic plankton forming the basis of the food web in the plankton community. Transfer of newly fixed nitrogen to diatoms and copepods furthermore implies a fast export to shallow sediments via fast-sinking fecal pellets and aggregates. Hence, N2-fixing colony-forming cyanobacteria can have profound impact on ecosystem productivity and biogeochemical processes at shorter time scales (hours to days) than previously thought.

National Category
Biological Sciences
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-122075 (URN)10.1038/ismej.2015.126 (DOI)000368561100015 ()
Available from: 2015-10-23 Created: 2015-10-23 Last updated: 2016-09-14Bibliographically approved
3. The bloom of nitrogen-fixing cyanobacteria in the northern Baltic Proper stimulates summer production
Open this publication in new window or tab >>The bloom of nitrogen-fixing cyanobacteria in the northern Baltic Proper stimulates summer production
2016 (English)In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 163, 102-112 p.Article in journal (Refereed) Published
Abstract [en]

In the northern Baltic Sea Proper, total nitrogen (TN) increases during the summer bloom of filamentous heterocystous cyanobacteria. To follow the fate of the nitrogen they fix, we studied several N fractions during the bloom. We measured cyanobacterial biomass, TN, particulate organic N (PON, two size fractions), dissolved organic N (DON), and PON sedimentation in two areas in 2011. TN increased mainly due to increasing PON, but also to DON. Cyanobacteria contributed about 20% of the PON increase and ~ 10% of the TN increase. About half the PON changes (increase, then decrease) could be explained by the sum of cyanobacteria, other autotrophs (> 2 μm) and zooplankton, indicating that the bloom stimulates primary and secondary production. TN decreased after the bloom mainly due to declining PON > 10 μm, but sedimentation rates did not increase and could explain little of the post-bloom N-loss. There was little settling of undecomposed cyanobacteria.

The seasonal development of Aphanizomenon sp. and N pools was similar among stations and areas. For Nodularia spumigena between-station variability increased once patchy surface accumulations developed. A brief Dolichospermum spp. bloom indicated that sampling frequency may be more important than spatial resolution for capturing dynamics of this bloom.

Keyword
Cyanobacteria, Nitrogen fixation, Nitrogen pools, Particulate and dissolved organic nitrogen, Secondary production, Sedimentation
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-132744 (URN)10.1016/j.jmarsys.2016.07.003 (DOI)
External cooperation:
Funder
Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 215-2009-813
Available from: 2016-08-22 Created: 2016-08-22 Last updated: 2016-08-30Bibliographically approved
4. Production and nitrogen fixation by Baltic Sea Aphanizomenon sp.  — estimates from a growth model
Open this publication in new window or tab >>Production and nitrogen fixation by Baltic Sea Aphanizomenon sp.  — estimates from a growth model
(English)Manuscript (preprint) (Other academic)
Keyword
cyanobacteria, Baltic Sea, nitrogen fixation, Aphanizomenon sp., growth model, photosynthesis-irradiance relationship, cell width
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-132753 (URN)
External cooperation:
Available from: 2016-08-22 Created: 2016-08-22 Last updated: 2016-09-02

Open Access in DiVA

Cyanobacterial Nitrogen Fixation in the Baltic Sea(1700 kB)21 downloads
File information
File name FULLTEXT01.pdfFile size 1700 kBChecksum SHA-512
a5f9d42a4877fd2481cee30e3403787b4d333e082268c6b86d6704eda38f360d0f30a818ccca21985f636ee1188d2cb463054c6dc0c3908aff9517c1ae3125a1
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Svedén, Jennie B.
By organisation
Department of Ecology, Environment and Plant Sciences
Ecology

Search outside of DiVA

GoogleGoogle Scholar
Total: 21 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 60 hits
ReferencesLink to record
Permanent link

Direct link