Salinity as a key control on the diazotrophic community composition in the southern Baltic Sea
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Published:2022-03-25
Issue:2
Volume:18
Page:401-417
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ISSN:1812-0792
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Container-title:Ocean Science
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language:en
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Short-container-title:Ocean Sci.
Author:
Reeder Christian FurboORCID, Stoltenberg Ina, Javidpour Jamileh, Löscher Carolin ReginaORCID
Abstract
Abstract. Over the next decade, the Baltic Sea is predicted to
undergo severe changes including decreased salinity due to altered
precipitation related to climate changes. This will likely impact the
distribution and community composition of Baltic Sea dinitrogen-fixing (N2-fixing)
microbes, among which heterocystous cyanobacteria are especially adapted
to low salinities and may expand to waters with currently higher salinity,
including the Danish Strait and Kattegat, while other high-salinity-adapted
N2 fixers might decrease in abundance. In order to explore the impact of salinity on the distribution and activity
of different diazotrophic clades, we followed the natural salinity gradient
from the eastern Gotland and Bornholm basins through the Arkona Basin to the
Kiel Bight and combined N2 fixation rate measurements with a molecular
analysis of the diazotrophic community using the key functional marker gene
for N2 fixation nifH, as well as the key functional marker genes anfD and vnfD,
encoding for the two alternative nitrogenases. We detected N2 fixation rates between 0.7 and 6 nmol N L−1 d−1, and the diazotrophic community was dominated by the cyanobacterium
related to Nodularia spumigena and the small unicellular, cosmopolitan cyanobacterium UCYN-A.
Nodularia was present in gene abundances between 8.07 × 105 and 1.6 × 107 copies L−1 in waters with salinities of 10 and below, while UCYN-A
reached gene abundances of up to 4.5 × 107 copies L−1 in waters
with salinity above 10. Besides those two cyanobacterial diazotrophs, we
found several clades of proteobacterial N2 fixers and alternative
nitrogenase genes associated with Rhodopseudomonas palustris, a purple non-sulfur bacterium. Based on
principal component analysis (PCA), salinity was identified as the primary
parameter describing the diazotrophic distribution, while pH and temperature
did not have a significant influence on the diazotrophic distribution. While
this statistical analysis will need to be explored in direct experiments, it
gives an indication for the future development of diazotrophy in a freshening
Baltic Sea with UCYN-A retracting to more saline North Sea waters and
heterocystous cyanobacteria expanding as salinity decreases.
Funder
Villum Fonden Horizon 2020
Publisher
Copernicus GmbH
Subject
Cell Biology,Developmental Biology,Embryology,Anatomy
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