High cell-specific rates of nitrogen and carbon fixation by the cyanobacterium Aphanizomenon sp. at low temperatures in the Baltic Sea.
Aphanizomenon is a widespread genus of nitrogen (N2)-fixing cyanobacteria in lakes and estuaries, accounting for a large fraction of the summer N2-fixation in the Baltic Sea. However, information about its cell-specific carbon (C)- and N2-fixation rates in the early growth season has not previously been reported. We combined various methods to study N2-fixation, photosynthesis and respiration in field-sampled Baltic Sea Aphanizomenon sp. during early summer at 10°C. Stable isotope incubations at in situ light intensities during 24 h combined with cell-specific secondary ion mass spectrometry showed an average net N2-fixation rate of 55 fmol N cell(-1) day(-1). Dark net N2-fixation rates over a course of 12 h were 20% of those measured in light. C-fixation, but not N2-fixation, was inhibited by high ambient light intensities during daytime. Consequently, the C:N fixation ratio varied substantially over the diel cycle. C- and N2-fixation rates were comparable to those reported for Aphanizomenon sp. in August at 19°C, using the same methods. High respiration rates (23% of gross photosynthesis) were measured with (14)C-incubations and O2-microsensors, and presumably reflect the energy needed for high N2-fixation rates. Hence, Aphanizomenon sp. is an important contributor to N2-fixation at low in situ temperatures in the early growth season.
Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-10691 Stockholm, Sweden jennie.sveden@su.se.
Jennie B
JB
Svedén
Max Planck Institute for Marine Microbiology, Celsiusstr. 1, DE-28359 Bremen, Germany.
Birgit
B
Adam
Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-10691 Stockholm, Sweden.
Jakob
J
Walve
Department of Marine Sciences, University of Gothenburg, Box 460, SE-405 30 Gothenburg, Sweden.
Nurun
N
Nahar
Max Planck Institute for Marine Microbiology, Celsiusstr. 1, DE-28359 Bremen, Germany Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research - UFZ, Permoserstr. 15, DE-04318 Leipzig, Germany.
Niculina
N
Musat
Max Planck Institute for Marine Microbiology, Celsiusstr. 1, DE-28359 Bremen, Germany.
Gaute
G
Lavik
Swedish Museum of Natural History, Box 50007, SE-10405 Stockholm, Sweden.
Martin J
MJ
Whitehouse
Max Planck Institute for Marine Microbiology, Celsiusstr. 1, DE-28359 Bremen, Germany.
Marcel M M
MM
Kuypers
Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-10691 Stockholm, Sweden Department of Marine Sciences, University of Gothenburg, Box 460, SE-405 30 Gothenburg, Sweden.
Helle
H
Ploug
D046890:Aphanizomenon / Q000145:classification / Q000302:isolation & purification / Q000378:metabolism*; D001454:Baltic States; D002244:Carbon / Q000378:metabolism; D057486:Carbon Cycle / Q000502:physiology*; D003080:Cold Temperature; D007553:Isotope Labeling; D008027:Light; D013058:Mass Spectrometry; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation / Q000502:physiology*; D010788:Photosynthesis; D012621:Seasons; D012623:Seawater / Q000382:microbiology*; D014871:Water Microbiology
D002244:Carbon; D009584:Nitrogen
Aphanizomenon; C-fixation; N2-fixation; O2-microsensors; SIMS; isotopes