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Dissolved Organic Matter Influences N2 Fixation in the New Caledonian Lagoon (Western Tropical South Pacific)

Abstract.

"Specialized prokaryotes performing biological dinitrogen (N2) fixation (“diazotrophs”) provide an important source of fixed nitrogen in oligotrophic marine ecosystems such as tropical and subtropical oceans. In these waters, cyanobacterial photosynthetic diazotrophs are well known to be abundant and active, yet the role and contribution of non-cyanobacterial diazotrophs are currently unclear. The latter are not photosynthetic (here called “heterotrophic”) and hence require external sources of organic matter to sustain N2 fixation.  [...]"

Source: Frontiers in Marine Science
Authors: Mar Benavides et al.
DOI: 10.3389/fmars.2018.00089

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Tiny microenvironments in the ocean hold clues to global nitrogen cycle

"Nitrogen is essential to marine life and cycles throughout the ocean in a delicately balanced system. Living organisms--especially marine plants called phytoplankton--require nitrogen in processes such as photosynthesis. In turn, phytoplankton growth takes up carbon dioxide from the atmosphere and helps regulate global climate. [...]"

Source: EruekAlert

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Latitudinal variations of δ30Si and δ15N signatures along the Peruvian shelf:

quantifying the effects of nutrient utilization versus denitrification over the past 600 years

Abstract. 

"The sedimentary stable nitrogen isotope compositions of bulk organic matter (δ15Nbulk) and silicon isotope composition of diatoms (δ30SiBSi) both mainly reflect the degree of past nutrient utilization by primary producers. However, in ocean areas where anoxic and suboxic conditions prevail, the δ15Nbulk signal ultimately recorded within the sediments is also influenced by water column denitrification causing an increase in the subsurface δ15N signature of dissolved nitrate (δ15NO3) upwelled to the surface. [...]"

Source: Biogeosciences
Authors: Kristin Doering et al.
DOI: 10.5194/bg-2018-118

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A missing link in the estuarine nitrogen cycle?: Coupled nitrification-denitrification mediated by suspended particulate matter

Abstract.

"In estuarine and coastal ecosystems, the majority of previous studies have considered coupled nitrification-denitrification (CND) processes to be exclusively sediment based, with little focus on suspended particulate matter (SPM) in the water column. Here, we present evidence of CND processes in the water column of Hangzhou Bay, one of the largest macrotidal embayments in the world. [...]"

Source: Scientific Reports
Authors: Weijing Zhu et al.
DOI: 10.1038/s41598-018-20688-4

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The microbial nitrogen-cycling network

Abstract.

"Nitrogen is an essential component of all living organisms and the main nutrient limiting life on our planet. By far, the largest inventory of freely accessible nitrogen is atmospheric dinitrogen, but most organisms rely on more bioavailable forms of nitrogen, such as ammonium and nitrate, for growth. [...]"

Source: Nature Reviews Microbiology
Authors: Marcel M. M. Kuypers, Hannah K. Marchant & Boran Kartal
DOI: 10.1038/nrmicro.2018.9

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Vertical segregation among pathways mediating nitrogen loss (N2 and N2O production) across the oxygen gradient in a coastal upwelling ecosystem

Abstract.

"The upwelling system off central Chile (36.5° S) is seasonally subjected to oxygen (O2)-deficient waters, with a strong vertical gradient in O2 (from oxic to anoxic conditions) that spans a few metres (30–50 m interval) over the shelf. This condition inhibits and/or stimulates processes involved in nitrogen (N) removal (e.g. anammox, denitrification, and nitrification). During austral spring (September 2013) and summer (January 2014), the main pathways involved in N loss and its speciation, in the form of N2 and/or N2O, were studied using 15N-tracer incubations, inhibitor assays, and the natural abundance of nitrate isotopes along with hydrographic information. [...]"

Source: Biogeosciences
Authors: Alexander Galán et al.
DOI: 10.5194/bg-14-4795-2017

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Temporal variation in pelagic food chain length in response to environmental change

Abstract.

"Climate variability alters nitrogen cycling, primary productivity, and dissolved oxygen concentration in marine ecosystems. We examined the role of this variability (as measured by six variables) on food chain length (FCL) in the California Current (CC) by reconstructing a time series of amino acid–specific δ15N values derived from common dolphins, an apex pelagic predator, and using two FCL proxies.  [...]"

Source: Science Advances
Authors: Rocio I. Ruiz-Cooley et al.
DOI: 10.1126/sciadv.1701140

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Oceanic nitrogen cycling and N2O flux perturbations in the Anthropocene

Abstract.

"There is currently no consensus on how humans are affecting the marine nitrogen (N) cycle, which limits marine biological production and CO2 uptake. Anthropogenic changes in ocean warming, deoxygenation, and atmospheric N deposition can all individually affect the marine N cycle and the oceanic production of the greenhouse gas nitrous oxide (N2O). However, the combined effect of these perturbations on marine N cycling, ocean productivity, and marine N2O production is poorly understood. Here we use an Earth system model of intermediate complexity to investigate the combined effects of estimated 21st century CO2 atmospheric forcing and atmospheric N deposition.  [...]"

Source: Global Biogeochemical Cycles
Authors: A. Landolfi, C. Somes, W. Koeve, L. M. Zamora, A. Oschlies
DOI: 10.1002/2017GB005633

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Differential effects of nitrate, ammonium, and urea as N sources for microbial communities in the North Pacific Ocean

Abstract.

"Nitrogen (N) is the major limiting nutrient for phytoplankton growth and productivity in large parts of the world's oceans. Differential preferences for specific N substrates may be important in controlling phytoplankton community composition. To date, there is limited information on how specific N substrates influence the composition of naturally occurring microbial communities. We investigated the effect of nitrate ( math formula), ammonium ( math formula), and urea on microbial and phytoplankton community composition (cell abundances and 16S rRNA gene profiling) and functioning (photosynthetic activity, carbon fixation rates) in the oligotrophic waters of the North Pacific Ocean. [...]"

Source: Limonology and Oceanography
Authors: I.N. Shilova et al.
DOI: 10.1002/lno.10590

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A three-dimensional model of the marine nitrogen cycle during the Last Glacial Maximum constrained by sedimentary isotopes

Abstract.

"Nitrogen is a key limiting nutrient that influences marine productivity and carbon sequestration in the ocean via the biological pump. In this study, we present the first estimates of nitrogen cycling in a coupled 3D ocean-biogeochemistry-isotope model forced with realistic boundary conditions from the Last Glacial Maximum (LGM) ~21,000 years before present constrained by nitrogen isotopes. The model predicts a large decrease in nitrogen loss rates due to higher oxygen concentrations in the thermocline and sea level drop, and, as a response, reduced nitrogen fixation. Model experiments are performed to evaluate effects of hypothesized increases of atmospheric iron fluxes and oceanic phosphorus inventory relative to present-day conditions. [...]"

Source: Frontiers in Marine Science
Authors: Christopher J. Somes et al.
DOI: 10.3389/fmars.2017.00108

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