Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Environmental conditions governing the distributions of symbiotic and free-living diazotrophic cyanobacteria in two tropical open oceans
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Di-nitrogen (N2) fixation plays a crucial role in oceanic carbon and nitrogen cycles and is important for marine biogeochemistry on regional and global scales. N2-fixing (diazotrophs) cyanobacteria are considered to contribute the most to marine nitrogen fixation, and thereby fuel the surrounding phytoplankton communities with bioavailable ammonia. Distribution and activity of phytoplankton, including diazotrophs, are largely driven by environmental conditions and temperature is often considered the main influence. A greater understanding of the environmental conditions that govern the diazotrophs, is vital to accurate predictions and estimations for the marine nitrogen budget, as well as understanding their impact on the nitrogen and carbon cycles.

Therefore, the primary aim of this thesis was to determine abundances and distribution patterns for various cyanobacterial diazotrophs in two different regions that in spite of their hydrological differences are prime regions for diazotrophy. Moreover, we attempted to identify the environmental conditions that govern cyanobacterial diazotrophs abundance.

In the first study we observed a clear separation of the unicellular diazotroph UCYN-A from the other diazotrophs, including the other unicellular types (UCYN-B, UCYN-C) in the Western Tropical South Pacific. The main driver of the vertical distribution of diazotrophs was based on a temperature-depth gradient, which was similar to the findings of our meta-analysis which included 11 additional datasets. Using newly and previously designed primers and probe sets for the UCYN-A1 and A2 hosts, we also observed discrepancies in detection and abundance for the two UCYN-A symbiotic strains (A1 and A2) and their respective hosts, which is in contrast to the current understanding of a highly specific and obligate partnership. Lastly, cross-hybridization tests revealed that the qPCR assay targeting the UCYN-A2 strain also enumerated UCYN-A1, demonstrating the difficulty in quantifying closely related strains.

In the second study we distinguished the environmental conditions favoring two closely related heterocystous cyanobacterial strains of Richelia intracellularis (het-1 and het-2) which associate with two different diatom hosts (Rhizosolenia and Hemiaulus, respectively) in the Western Tropical North Atlantic (WTNA). In general, the Amazon River (AR) plume heavily influenced het-1 and het-2 abundances; higher densities were quantified at stations with mesohaline sea surface salinities and maximum abundances were detected in the sub-surface, below the freshwater discharge. However, maximum abundances at oceanic sea surface salinity stations were observed nearer to the surface. A piecewise Structural Equation Model (SEM) was developed and identified turbidity as an important factor governing het-1 and het-2 abundance. In addition, het-1 and het-2 distribution pattern was influenced by dissolved inorganic phosphorus (DIP) concentration and salinity. Het-1 tended to penetrate deeper waters and was favored by increased salinity, while the opposite was true for het-2.

The results of this thesis contribute to a better understanding of marine cyanobacterial diazotrophs’ ecological niches and will prove useful in future predictions and research on nitrogen fixation, and the role of cyanobacterial diazotrophs in marine biogeochemistry.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University , 2017. , 39 p.
Keyword [en]
Nitrogen fixation, Diazotroph, Cyanobacteria, Symbiosis, DDA, Richelia
National Category
Ecology
Research subject
Marine Ecology; Microbiology
Identifiers
URN: urn:nbn:se:su:diva-143059OAI: oai:DiVA.org:su-143059DiVA: diva2:1094479
Presentation
2017-05-31, P216, Svante Arrhenius väg 20 A, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2017-06-19 Created: 2017-05-10 Last updated: 2017-06-19Bibliographically approved

Open Access in DiVA

Stenegren Licentiate Thesis 2017(1751 kB)1 downloads
File information
File name SUMMARY01.pdfFile size 1751 kBChecksum SHA-512
4afe49e399bc5de939cd6a41de023a5090562576ddb855bfd78ffd2105b9629810c1765e6b3df039155a5a66c7613ccc28b1c8792094505f4734f10cadeea03e
Type summaryMimetype application/pdf

Search in DiVA

By author/editor
Stenegren, Marcus
By organisation
Department of Ecology, Environment and Plant Sciences
Ecology

Search outside of DiVA

GoogleGoogle Scholar
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: 6 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf