TY - JOUR
T1 - Significant N2 fixation by heterotrophs, photoheterotrophs and heterocystous cyanobacteria in two temperate estuaries
AU - Bentzon-Tilia, Mikkel
AU - Traving, Sachia Jo
AU - Mantikci, Mustafa
AU - Knudsen-Leerbeck, Helle
AU - Hansen, Jørgen L.S.
AU - Markager, Stiig
AU - Riemann, Lasse
PY - 2015/2/22
Y1 - 2015/2/22
N2 - Nitrogen (N) fixation is fueling planktonic production in a multitude of aquatic environments. In meso- and poly-haline estuaries, however, the contribution of N by pelagic N 2 fixation is believed to be insignificant due to the high input of N from land and the presumed absence of active N 2 -fixing organisms. Here we report N 2 fixation rates, nifH gene composition and nifH gene transcript abundance for key diazotrophic groups over 1 year in two contrasting, temperate, estuarine systems: Roskilde Fjord (RF) and the Great Belt (GB) strait. Annual pelagic N 2 fixation rates averaged 17 and 61 mmol N m -2 per year at the two sites, respectively. In RF, N 2 fixation was mainly accompanied by transcripts related to heterotrophic (for example, Pseudomonas sp.) and photoheterotrophic bacteria (for example, unicellular diazotrophic cyanobacteria group A). In the GB, the first of two N 2 fixation peaks coincided with a similar nifH-expressing community as in RF, whereas the second peak was synchronous with increased nifH expression by an array of diazotrophs, including heterotrophic organisms as well as the heterocystous cyanobacterium Anabaena. Thus, we show for the first time that significant planktonic N 2 fixation takes place in mesohaline, temperate estuaries and that the importance of heterotrophic, photoheterotrophic and photosynthetic diazotrophs is clearly variable in space and time.
AB - Nitrogen (N) fixation is fueling planktonic production in a multitude of aquatic environments. In meso- and poly-haline estuaries, however, the contribution of N by pelagic N 2 fixation is believed to be insignificant due to the high input of N from land and the presumed absence of active N 2 -fixing organisms. Here we report N 2 fixation rates, nifH gene composition and nifH gene transcript abundance for key diazotrophic groups over 1 year in two contrasting, temperate, estuarine systems: Roskilde Fjord (RF) and the Great Belt (GB) strait. Annual pelagic N 2 fixation rates averaged 17 and 61 mmol N m -2 per year at the two sites, respectively. In RF, N 2 fixation was mainly accompanied by transcripts related to heterotrophic (for example, Pseudomonas sp.) and photoheterotrophic bacteria (for example, unicellular diazotrophic cyanobacteria group A). In the GB, the first of two N 2 fixation peaks coincided with a similar nifH-expressing community as in RF, whereas the second peak was synchronous with increased nifH expression by an array of diazotrophs, including heterotrophic organisms as well as the heterocystous cyanobacterium Anabaena. Thus, we show for the first time that significant planktonic N 2 fixation takes place in mesohaline, temperate estuaries and that the importance of heterotrophic, photoheterotrophic and photosynthetic diazotrophs is clearly variable in space and time.
U2 - 10.1038/ismej.2014.119
DO - 10.1038/ismej.2014.119
M3 - Journal article
C2 - 25026373
SN - 1751-7362
VL - 9
SP - 273
EP - 285
JO - I S M E Journal
JF - I S M E Journal
ER -