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Regulation of heterocyst frequency in Baltic Sea Aphanizomenon sp.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
2014 (English)In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 36, no 5, 1357-1367 p.Article in journal (Refereed) Published
Abstract [en]

Heterocyst frequencies in Baltic Sea Aphanizomenon sp. were similar along a strong nutrient gradient from the discharge point of a sewage treatment plant at the head of the Himmerfjarden bay to the open sea. Filaments lacked heterocysts in winter and for over a month after the spring bloom had depleted combined nitrogen in the surface layer. Heterocyst-free filaments in spring contained granulate structures that decreased in abundance simultaneously as colony nitrogen content decreased, but delta N-15 remained unchanged, indicative of storage of fixed nitrogen in over-wintering Aphanizomenon sp. filaments. Heterocyst formation was initiated when water temperature was sufficient to form a shallow seasonal pycnocline that allowed filaments to be exposed to enough light to initiate growth and a subsequent intracellular shortage of nitrogen. During the growth season, heterocyst frequency varied significantly with maximum values in early summer (May), lower values in mid-August that coincided with maximum temperatures and an increase in late summer. Heterocyst frequencies decreased with increased temperatures, suggesting a more efficiently functioning nitrogenase enzyme. Based on data from three seasons, filament C: P ratios did not correlate with heterocyst frequencies, neither did reduced heterocyst frequencies coincide with high dissolved inorganic nitrogen concentrations. Increased heterocyst frequencies, however, resulted in decreased C:N ratios, probably as more heterocysts likely increase nitrogen fixation.

Place, publisher, year, edition, pages
2014. Vol. 36, no 5, 1357-1367 p.
Keyword [en]
Aphanizomenon sp., heterocysts, cyanobacteria, diazotrophs, Baltic Sea proper
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:su:diva-108379DOI: 10.1093/plankt/fbu055ISI: 000342235000016OAI: oai:DiVA.org:su-108379DiVA: diva2:758095
Note

AuthorCount:2;

Available from: 2014-10-24 Created: 2014-10-22 Last updated: 2017-12-05Bibliographically approved
In thesis
1. External Growth Control of Baltic Sea Cyanobacteria
Open this publication in new window or tab >>External Growth Control of Baltic Sea Cyanobacteria
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In the Himmerfjärden Bay a large excess of nitrogen over phosphorus in the discharge from a large sewage treatment plant (STP) has suppressed growth of diazotrophic cyanobacteria in its inner parts. Implementation of nitrogen removal in the STP in 1997 drastically reduced nitrogen load and triggered growth of diazotrophs, mainly Aphanizomenon sp. This study is part of a long-term series of experiments with the overall aim to test how algal biomass and production in a receiving area can be reduced, without stimulating nitrogen fixation and biomass growth by diazotrophic cyanobacteria. Nitrogen removal was discontinued in the STP during two years (2007-8) and resumed in 2009, and the discharge shifted from 25 to 10 m depth, above the seasonal pycnocline. Cellular 15N showed that N2 was the most important N source for diazotrophic cyanobacteria, and that uptake of combined nitrogen was insignificant. As biomass was declining and at the end of the productive season, we could detect a small, but significant, increase in cellular δ15N at the inner bay stations (H3 and H4). However, this coincided with an increased proportion of Anabaena spp. of the total diazotrophic biomass. This may indicate that Anabaena spp. has a higher uptake of combined nitrogen compared with Aphanizomenon sp. or that declining populations of Aphanizomenon sp. take up combined nitrogen. We also found no evidence of uptake of combined nitrogen during the winter months when nitrogen supply is ample and Aphanizomenon sp. is devoid of heterocysts. During the first half of summer (week 21-27) heterocyst frequencies were higher at the outer stations B1 and H2, compared to the inner bay stations (H4 and H5). The lower frequencies at the inner bay stations are likely due to the reduced growth rate suffered by the Aphanizomenon sp. due to stronger competition for phosphorus by non-diazotrophs at these stations and hence lower need for heterocysts. Towards the end of summer conditions even out along the bay, as the surplus phosphorus from the spring bloom is used up at the outer stations and no heterocyst gradient is present. Heterocyst frequency varied significantly over the summer, with minimum values in the beginning of July, coinciding with the highest water temperatures, and higher frequencies in early and late summer. We suggest this is primarily due to a more efficiently functioning nitrogenase enzyme at high temperatures with a reduced need for “expensive” heterocysts. Spring heterocyst differentiation occurred around 4-6 weeks after depletion of dissolved inorganic nitrogen (DIN) and only when water temperature was 5-9 oC and a pycnocline established. It seems that temperature and light in concert will initiate growth, leading to an internal nitrogen deficiency which starts heterocyst differentiation.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, 2013. 21 p.
Series
Licentiate in Philosophy Thesis / Department of Ecology, Environment and Plant Sciences, ISSN 1401-4106 ; 2013:1
Keyword
Baltic Sea, cyanobacteria, nitrogen fixation, heterocysts, Aphanizomenon, Nodularia, water treatment, Himmerfjärden, sewage, climate
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-90086 (URN)
Presentation
2013-05-30, Room 107, Dept. Ecology, Environment and Plant Sciences, Frescati Backe, Svante Arrheniusv. 21A, Stockholm, 11:53 (English)
Opponent
Supervisors
Projects
Himmerfjärden eutrophication study
Available from: 2013-05-22 Created: 2013-05-22 Last updated: 2017-11-22Bibliographically approved
2. External Growth Control of Baltic Sea Cyanobacteria
Open this publication in new window or tab >>External Growth Control of Baltic Sea Cyanobacteria
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The overall aim of the study was to provide better insights to the ecological role and impact of cyanobacteria in Baltic Sea (BS) bay, coastal and open sea areas. Biomass and heterocyst development of diazotrophic, heterocystous cyanobacteria were monitored over several years simultaneously as physical parameters such as nutrients and temperature. Nitrogen fixation was estimated as well as its transfer in the BS food web. Even after decades of debate there is still controversy whether eutrophication of lakes and estuaries/coastal areas should be managed by reducing phosphorus only or also nitrogen. Central to this debate is whether nitrogen fixation by cyanobacteria can replace shortages of combined nitrogen quickly enough to make phosphorus the limiting nutrient and nitrogen removal pointless or even harmful. Also, it is not clear if available combined nitrogen inhibits heterocystous cyanobacterial nitrogen fixation and if it is used for their growth in situ. A large ecosystem-wide experiment started in Himmerfjärden bay in year 1997, where the N-loadings and release depth from a modern sewage treatment plant (STP), located in the inner part of the bay, were modulated. The STP creates a steep gradient of nutrients and stable nitrogen isotopes, which can be used to study uptake of combined nitrogen, as well as biomass development and primary productivity. A 35-year long data series was used to achieve good insights into phytoplankton development and primary productivity in the Baltic Sea over the last couple of decades. These in vivo long time series, based on monitoring data, in combination with shorter series (2-3 seasons, including measurements of colony stoichiometry and stable isotopes), have resulted in a unique meta-dataset, allowing for high-resolution observations into the role of the cyanobacteria in the Baltic Sea ecosystem.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2015. 47 p.
Keyword
Cyanobacteria, Baltic Sea, diazotrophs, diazotrophy, heterocysts, primary productivity, stable isotopes, sewage treatment
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-112753 (URN)978-91-7649-086-0 (ISBN)
Public defence
2015-03-20, The Lecure Hall, Department of Ecology, Environment and Plant Sciences, Lilla Frescativägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council Formas
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2015-02-26 Created: 2015-01-14 Last updated: 2015-06-30Bibliographically approved

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