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High cell-specific rates of nitrogen and carbon fixation by the cyanobacterium Aphanizomenon sp. at low temperatures in the Baltic Sea.

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Title: High cell-specific rates of nitrogen and carbon fixation by the cyanobacterium Aphanizomenon sp. at low temperatures in the Baltic Sea.
Authors: Svedén, Jennie B.1 jennie.sveden@su.se, Adam, Birgit1, Walve, Jakob2, Nahar, Nurun1, Musat, Niculina3, Lavik, Gaute2,4, Whitehouse, Martin J.2, Kuypers, Marcel M. M.5, Ploug, Helle1,3
Source: FEMS Microbiology Ecology. Dec2015, Vol. 91 Issue 12, p1-10. 10p. 1 Color Photograph, 3 Charts, 5 Graphs.
Subjects: Aphanizomenon, Low temperatures, Cyanobacteria, Secondary ion mass spectrometry, Photosynthesis, Carbon fixation
Geographic Terms: Baltic Sea
Abstract: 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 14C-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. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract: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 14C-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. [ABSTRACT FROM AUTHOR]
ISSN:01686496
DOI:10.1093/femsec/fiv131