title: Cell-specific nitrogen- and carbon-fixation of cyanobacteria in a temperate marine system (Baltic Sea).
abstract: We analysed N2- and carbon (C) fixation in individual cells of Baltic Sea cyanobacteria by combining stable isotope incubations with secondary ion mass spectrometry (SIMS). Specific growth rates based on N2- and C-fixation were higher for cells of Dolichospermum spp. than for Aphanizomenon sp. and Nodularia spumigena. The cyanobacterial biomass, however, was dominated by Aphanizomenon sp., which contributed most to total N2-fixation in surface waters of the Northern Baltic Proper. N2-fixation by Pseudanabaena sp. and colonial picocyanobacteria was not detectable. N2-fixation by Aphanizomenon sp., Dolichospermum spp. and N. spumigena populations summed up to total N2-fixation, thus these genera appeared as sole diazotrophs within the Baltic Sea's euphotic zone, while their mean contribution to total C-fixation was 21%. Intriguingly, cell-specific N2-fixation was eightfold higher at a coastal station compared to an offshore station, revealing coastal zones as habitats with substantial N2-fixation. At the coastal station, the cell-specific C- to N2-fixation ratio was below the cellular C:N ratio, i.e. N2was assimilated in excess to C-fixation, whereas the C- to N2-fixation ratio exceeded the C:N ratio in offshore sampled diazotrophs. Our findings highlight SIMS as a powerful tool not only for qualitative but also for quantitative N2-fixation assays in aquatic environments.
authors.affiliation: Department of Ecology, Environment and Plant Sciences Stockholm University, Stockholm, Sweden.
authors.forename: I
authors.initials: I
authors.lastname: Klawonn
authors.affiliation: Department of Biology and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden.
authors.forename: N
authors.initials: N
authors.lastname: Nahar
authors.affiliation: Department of Ecology, Environment and Plant Sciences Stockholm University, Stockholm, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Walve
authors.affiliation: Department of Biology and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Andersson
authors.affiliation: Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Olofsson
authors.affiliation: Department of Ecology, Environment and Plant Sciences Stockholm University, Stockholm, Sweden.
authors.forename: J B
authors.initials: JB
authors.lastname: Svedén
authors.affiliation: Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Littmann
authors.affiliation: Swedish Museum of Natural History, Stockholm, Sweden.
authors.forename: M J
authors.initials: MJ
authors.lastname: Whitehouse
authors.affiliation: Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: M M M
authors.initials: MM
authors.lastname: Kuypers
authors.affiliation: Department of Ecology, Environment and Plant Sciences Stockholm University, Stockholm, Sweden.|Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Ploug
mesh_terms: D046890:Aphanizomenon / Q000378:metabolism; D001454:Baltic States; D002244:Carbon / Q000378:metabolism; D057486:Carbon Cycle; D000458:Cyanobacteria / Q000145:classification / Q000378:metabolism*; D017753:Ecosystem; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation; D046932:Nodularia / Q000378:metabolism; D009792:Oceans and Seas; D012623:Seawater / Q000382:microbiology; D018629:Spectrometry, Mass, Secondary Ion
chemical_list: D002244:Carbon; D009584:Nitrogen