Nitrogen fixation by cyanobacteria stimulates production in Baltic food webs

Karlson, Agnes M. L.; Duberg, Jon; Motwani, Nisha H.; Hogfors, Hedvig; Klawonn, Isabell; Ploug, Helle; Svedén, Jennie B.; Garbaras, Andrius; Sundelin, Brita; Hajdu, Susanna; Larsson, Ulf; Elmgren, Ragnar; Gorokhova, Elena

doi:10.1007/s13280-015-0660-x

Cited by 98 publications

(93 citation statements)

References 87 publications

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“…Hence, we consider our data to be robust and not compromised by contaminations in the added 15 N 2 gas. Simultaneous measurements of C-and N 2 -fixation rates in the Baltic Proper have suggested that N 2 -fixation supports 5-37% of the N-demand for the measured C-fixation by the whole phytoplankton community assuming a C:N molar ratio of 6.6 in phytoplankton (Karlson et al, 2015). In the present study, NH 4 + release by Aphanizomenon was substantial although we did not measure any high accumulation of 15 NH 4 + in the bulk water during our 15 N 2 -fixation experiments.…”

Section: Discussionmentioning

confidence: 99%

“…Experimental studies as well as nitrogen budgets have suggested that N 2 -fixing cyanobacteria leak a substantial fraction of their fixed nitrogen that is subsequently assimilated by picoplankton in the Baltic Sea (Ohlendieck et al, 2000;Larsson et al, 2001;Stal et al, 2003). Various routes by which diazotrophic nitrogen may enter the pelagic food web have been investigated indirectly through experimental studies and by using the natural abundance (δ 15 N) signature of N 2 -fixation in field studies (Wannicke et al, 2013;Woodland et al, 2013;Lesutiene et al, 2014;Karlson et al, 2015). Direct measurements of the routes and overall significance of N release by N 2 -fixing cyanobacteria and subsequent N uptake within the phytoplankton community are missing, largely owing to technical and methodological limitations.…”

Section: Introductionmentioning

confidence: 99%

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N2-fixation, ammonium release and N-transfer to the microbial and classical food web within a plankton community

et al. 2015

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We investigated the role of N 2 -fixation by the colony-forming cyanobacterium, Aphanizomenon spp., for the plankton community and N-budget of the N-limited Baltic Sea during summer by using stable isotope tracers combined with novel secondary ion mass spectrometry, conventional mass spectrometry and nutrient analysis. + fluxes to Aphanizomenon colonies at low bulk concentrations (o250 nM) as compared with N 2 -fixation within colonies. No N 2 -fixation was detected in autotrophic microorganisms o5 μm, which relied on NH 4 + uptake from the surrounding water. Aphanizomenon released about 50% of its newly fixed N 2 as NH 4 + . However, NH 4 + did not accumulate in the water but was transferred to heterotrophic and autotrophic microorganisms as well as to diatoms (Chaetoceros sp.) and copepods with a turnover time of 5 h. We provide direct quantitative evidence that colony-forming Aphanizomenon releases about half of its recently fixed N 2 as NH 4 + , which is transferred to the prokaryotic and eukaryotic plankton forming the basis of the food web in the plankton community. Transfer of newly fixed nitrogen to diatoms and copepods furthermore implies a fast export to shallow sediments via fast-sinking fecal pellets and aggregates. Hence, N 2 -fixing colony-forming cyanobacteria can have profound impact on ecosystem productivity and biogeochemical processes at shorter time scales (hours to days) than previously thought.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

N2-fixation, ammonium release and N-transfer to the microbial and classical food web within a plankton community

et al. 2015

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“…Thus, apart from such harmful effects of cyanobacteria blooms as degradation of recreational potential and increased water toxicity, this selfsupporting vicious circle (Vahtera et al, 2007a,b) counteracts nitrogen load reduction efforts and causes other ecosystem effects generated and sustained by hypoxia, including damage to cod reproduction and condition (MacKenzie et al, 2000;Casini et al, 2016). On the other hand, the cyanobacteria blooms stimulate summer production in the entire food web, from zooplankton and benthos to fish (Karlson et al, 2015;Svedén et al, 2016).…”

Section: The Vicious Circlementioning

confidence: 99%

Large-Scale Nutrient Dynamics in the Baltic Sea, 1970–2016

2018

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The Baltic Sea is one of the world's marine areas well-covered by both long-term observations and oceanographic studies. It is also a large coastal area in which eutrophication had already been recognized half a century ago. While the mechanisms of eutrophication are largely understood, several features are less recognized and sometimes neglected, including: (a) natural and anthropogenic North-South and East-West nutrient gradients within the drainage basin and marine ecosystems; (b) the compensatory potential of the interconnectivity between the Baltic Sea basins; (c) long nutrient residence times and high buffer capacity of the system, resulting in slow responses to nutrient load reductions. Particularly important is the interaction of (d) naturally occurring saltwater inflows sporadically ventilating deep water layers and (e) a partly man-made intensification of biological oxygen consumption. Resulting redox alterations of biogeochemical nitrogen and phosphorus cycles are locked in a "vicious circle" that promotes cyanobacterial nitrogen fixation, thereby hindering nitrogen load reduction and sustaining an elevated trophic state. This tight coupling of natural environmental variation and human impacts complicates both scientific studies and management recommendations. Our primary objective is to describe all these features and mechanisms with the best available data on nutrient loads, and unique estimates of the basin-wide nutrient pools. These data are presented as both long-term time series and empirical nutrient budgets. The analysis is supplemented by results of biogeochemical modeling. A second, more practical objective is to make these time series available to the community.

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“…Their ability to fix nitrogen makes them important in driving the nitrogen cycle and stimulating summer primary production (e.g., Larsson et al, 2001;Karlson et al, 2015). The propensity of the co-dominant genus Nodularia to form dense surface accumulations makes it feasible to map their distribution using satellite sensors, including some not specifically designed for ocean color applications (Kahru and Elmgren, 2014).…”

Section: Frequency Of Cyanobacteria Surface Accumulationsmentioning

confidence: 99%

Changing seasonality of the Baltic Sea

2016

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Abstract. Changes in the phenology of physical and ecological variables associated with climate change are likely to have significant effect on many aspects of the Baltic ecosystem. We apply a set of phenological indicators to multiple environmental variables measured by satellite sensors for 17-36 years to detect possible changes in the seasonality in the Baltic Sea environment. We detect significant temporal changes, such as earlier start of the summer season and prolongation of the productive season, in several variables ranging from basic physical drivers to ecological status indicators. While increasing trends in the absolute values of variables like sea-surface temperature (SST), diffuse attenuation of light (Ked490) and satellite-detected chlorophyll concentration (CHL) are detectable, the corresponding changes in their seasonal cycles are more dramatic. For example, the cumulative sum of 30 000 W m −2 of surface incoming shortwave irradiance (SIS) was reached 23 days earlier in 2014 compared to the beginning of the time series in 1983. The period of the year with SST of at least 17 • C has almost doubled (from 29 days in 1982 to 56 days in 2014), and the period with Ked490 over 0.4 m −1 has increased from about 60 days in 1998 to 240 days in 2013 -i.e., quadrupled. The period with satellite-estimated CHL of at least 3 mg m −3 has doubled from approximately 110 days in 1998 to 220 days in 2013. While the timing of both the phytoplankton spring and summer blooms have advanced, the annual CHL maximum that in the 1980s corresponded to the spring diatom bloom in May has now shifted to the summer cyanobacteria bloom in July.

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Nitrogen fixation by cyanobacteria stimulates production in Baltic food webs

Cited by 98 publications

References 87 publications

N2-fixation, ammonium release and N-transfer to the microbial and classical food web within a plankton community

N2-fixation, ammonium release and N-transfer to the microbial and classical food web within a plankton community

Large-Scale Nutrient Dynamics in the Baltic Sea, 1970–2016

Changing seasonality of the Baltic Sea

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