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Related Concept Videos

Microbes and the Nitrogen Cycle01:26

Microbes and the Nitrogen Cycle

The nitrogen cycle is a complex biogeochemical process critical to maintaining the balance of nitrogenous compounds in ecosystems. This cycle involves multiple microbial-mediated transformations through which nitrogen changes oxidation states, supporting essential ecological functions and contributing to plant and microbial growth.Nitrogen Fixation and AmmonificationNitrogen fixation initiates the cycle by converting inert atmospheric nitrogen (N₂) into bioavailable ammonia (NH₃), a process...
Overview of Nitrogen Metabolism01:20

Overview of Nitrogen Metabolism

Nitrogen is a very important element for life because it is a major constituent of proteins and nucleic acids. It is a macronutrient, and in nature, it is recycled from organic compounds and stored in the form of  ammonia, ammonium ions, nitrate, nitrite, or  nitrogen gas by many metabolic processes. Many of these metabolic processes are carried out only by prokaryotes.
The largest pool of nitrogen available in the terrestrial ecosystem is gaseous nitrogen (N2) from the air, but this nitrogen...
Carbon-dioxide Fixation01:28

Carbon-dioxide Fixation

Carbon dioxide fixation in prokaryotes enables the assimilation of inorganic carbon into organic molecules, supporting biosynthetic pathways, sustaining ecosystems, and contributing to the global carbon cycle. It also has industrial applications in carbon capture and bioproduct synthesis. Autotrophic organisms rely on this process to utilize CO₂ as a carbon source in diverse environments.The Calvin CycleThe Calvin cycle is the most widespread carbon fixation mechanism, primarily used by...
Inorganic Nitrogen Assimilation01:22

Inorganic Nitrogen Assimilation

Nitrogen is an essential element in biological systems, forming a crucial component of proteins, nucleic acids, and other cellular constituents. Many bacteria and archaea acquire nitrogen in the form of nitrate (NO₃⁻) or ammonia (NH₃), which are then assimilated into biomolecules through specific enzymatic pathways.Assimilatory Nitrate ReductionWhen nitrate enters the cell, it undergoes a two-step reduction process known as assimilatory nitrate reduction. Initially, the enzyme nitrate reductase...
The Nitrogen Cycle01:49

The Nitrogen Cycle

Nitrogen atoms, present in all proteins and DNA, are recycled between abiotic and biotic components of the ecosystem. However, the primary form of nitrogen on Earth is nitrogen gas, which cannot be used by most animals and plants. Thus, nitrogen gas must first be converted into a usable form by nitrogen-fixing bacteria before it can be cycled through other living organisms. The use of nitrogen-containing fertilizers and animal waste products in human agriculture has greatly influenced the...
Marine Microbial Ecology01:30

Marine Microbial Ecology

Marine microbial ecosystems are shaped by distinct physicochemical limits, including high salinity, low nutrient availability, and fluctuating oxygen levels. These conditions favor smaller microbial cell sizes, which maximize their surface-to-volume ratio for efficient nutrient uptake.Microbial activity and community composition are closely linked to biogeochemical cycles, particularly in dynamic environments like estuaries, where halotolerant microbes thrive in response to variable salinity...

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Related Experiment Video

Updated: Jul 12, 2026

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O
08:05

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O

Published on: October 7, 2020

Nitrogen fixation in the marine environment.

D G Capone, E J Carpenter

    Science (New York, N.Y.)
    |September 17, 1982
    PubMed
    Summary
    This summary is machine-generated.

    Marine nitrogen fixation by cyanobacteria and benthic environments is significant but insufficient to support phytoplankton growth. This suggests other factors, not nitrogen limitation, control phytoplankton productivity in the oceans.

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    The Benthic Exchange of O2, N2 and Dissolved Nutrients Using Small Core Incubations
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    Estimating Sediment Denitrification Rates Using Cores and N2O Microsensors
    07:59

    Estimating Sediment Denitrification Rates Using Cores and N2O Microsensors

    Published on: December 6, 2018

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    Last Updated: Jul 12, 2026

    Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O
    08:05

    Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O

    Published on: October 7, 2020

    The Benthic Exchange of O2, N2 and Dissolved Nutrients Using Small Core Incubations
    10:11

    The Benthic Exchange of O2, N2 and Dissolved Nutrients Using Small Core Incubations

    Published on: August 3, 2016

    Estimating Sediment Denitrification Rates Using Cores and N2O Microsensors
    07:59

    Estimating Sediment Denitrification Rates Using Cores and N2O Microsensors

    Published on: December 6, 2018

    Area of Science:

    • Marine biology
    • Oceanography
    • Biogeochemistry

    Background:

    • Nitrogen fixation is crucial for marine ecosystems, with cyanobacteria (e.g., Trichodesmium) and benthic environments being key contributors.
    • Estimates suggest oceanic nitrogen fixation is a fraction of terrestrial fixation and industrial ammonia synthesis.
    • The marine nitrogen cycle is considered to be in a steady state when inputs are balanced against denitrification losses.

    Purpose of the Study:

    • To quantify the contribution of oceanic nitrogen fixation to the global nitrogen budget.
    • To assess the adequacy of oceanic nitrogen fixation in meeting the nitrogen demands of marine phytoplankton.
    • To investigate the implications of nitrogen fixation rates for the understanding of phytoplankton growth limitation.

    Main Methods:

    • Quantitative analysis of nitrogen input from Oscillatoria (Trichodesmium) and benthic environments.
    • Comparison of oceanic nitrogen fixation rates with terrestrial fixation and industrial ammonia production.
    • Evaluation of nitrogen fixation's contribution relative to phytoplankton nitrogen demand.
    • Assessment of the marine nitrogen cycle's steady state by comparing inputs and denitrification losses.

    Main Results:

    • Oscillatoria (Trichodesmium) contributes approximately 4.8 x 10^12 grams of nitrogen annually to oceans.
    • Benthic environments contribute about 15 x 10^12 grams of nitrogen annually.
    • Oceanic nitrogen fixation supplies less than 0.3% of the nitrogen required by marine phytoplankton.
    • The marine nitrogen cycle approximates a steady state, balancing inputs and denitrification.

    Conclusions:

    • Nitrogen fixation, while substantial, is a minor contributor to the overall marine nitrogen economy.
    • The limited contribution of nitrogen fixation challenges the notion that nitrogen is the primary limiting nutrient for phytoplankton.
    • Factors other than nitrogen availability likely limit phytoplankton growth rates in the ocean.