Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in ISME Journal 9 (2015): 1635–1647, doi:10.1038/ismej.2014.253.
Description:
Symbiotic relationships between phytoplankton and N2-fixing microorganisms
play a crucial role in marine ecosystems. The abundant and widespread unicellular
cyanobacteria group A (UCYN-A) has recently been found to live symbiotically with
a haptophyte. Here, we investigated the effect of nitrogen (N), phosphorus (P), iron
(Fe) and Saharan dust additions on nitrogen (N2) fixation and primary production by
the UCYN-A-haptophyte association in the subtropical eastern North Atlantic Ocean
using nifH expression analysis and stable isotope incubations combined with single
cell measurements. N2 fixation by UCYN-A was stimulated by the addition of Fe and
Saharan dust although this was not reflected in the nifH expression. CO2 fixation by
the haptophyte was stimulated by the addition of ammonium nitrate as well as Fe and
Saharan dust. Intriguingly, the single-cell analysis using nanoSIMS indicates that the
increased CO2 fixation by the haptophyte in treatments without added fixed N is likely
an indirect result of the positive effect of Fe and/or P on UCYN-A N2 fixation and the
transfer of N2-derived N to the haptophyte. Our results reveal a direct linkage between
the marine carbon and nitrogen cycles that is fuelled by the atmospheric deposition of
dust. The comparison of single-cell rates suggests a tight coupling of nitrogen and
carbon transfer that stays balanced even under changing nutrient regimes. However, it
appears that the transfer of carbon from the haptophyte to UCYN-A requires a transfer
of nitrogen from UCYN-A. This tight coupling indicates an obligate symbiosis of this
globally important diazotrophic association.
Description:
We thank Surface Ocean Processes in the Anthropocene
(Sopran) and the Sonderforschungsbereich SFB754 for financial support. This study
was funded by the Max Planck Society.
Keywords:
Diazotrophs
;
Double CARD–FISH
;
N2 fixation
;
NanoSIMS
;
Saharan dust
;
Single–cell
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
Permalink
