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Definition: nitrogen cycle from Dictionary of Energy

Earth Science. the continuous process by which nitrogen circulates among the air, soil, water, plants, and animals of the earth. In a specific cycle, nitrogen in the atmosphere is converted by bacteria into substances that green plants can absorb from the soil; animals then eat these plants (or eat other animals that feed on the plants); the animals and plants then die and decay; the nitrogenous substances in the decomposed organic matter then return to the atmosphere and the soil.

nitrogen cycle

From The Columbia Encyclopedia
the continuous flow of nitrogen through the biosphere by the processes of nitrogen fixation, ammonification (decay), nitrification, and denitrification. Nitrogen is vital to all living matter, both plant and animal; it is an essential constituent of amino acids, which form proteins of nucleic acids , and of many other organic materials. Although the earth's atmosphere is 78% nitrogen, free gaseous nitrogen cannot be utilized by animals or by higher plants. They depend instead on nitrogen that is present in the soil. To enter living systems, nitrogen must be “fixed” (combined with oxygen or hydrogen) into compounds that plants can utilize, such as nitrates or ammonia. A certain amount of atmospheric nitrogen is fixed by lightning and by some cyanobacteria (blue-green algae). But the great bulk of nitrogen fixation is performed by soil bacteria of two kinds: those that live free in the soil and those that live enclosed in nodules in the roots of certain leguminous plants (e.g., alfalfa, …
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Full text Article nitrogen cycle

From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide
Process of nitrogen passing through the ecosystem. Nitrogen, in the form of inorganic compounds (such as nitrates) in the soil, is absorbed by plants and turned into organic compounds (such as proteins) in plant tissue. A proportion of this nitrogen is eaten by herbivores , with some of this in turn…
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Full text Article nitrogen cycle

From Penguin Dictionary of Biology
Circulation of nitrogen atoms, brought about mainly by living organisms. Inorganic nitrogenous compounds (chiefly nitrates) are absorbed by autotrophic plants from soil or water and synthesized into organic compounds. These autotrophs die and decay or are eaten by animals, and the nitrogen, still in…
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Full text Article nitrogen cycle

From The Macquarie Dictionary
the continuous circulation of nitrogen and nitrogen compounds in nature between the atmosphere, the soil, and the various organisms to which nitrogen is essential. Plural: nitrogen cycles The nitrogen cycle describes the complex movement of nitrogen between the atmosphere where it exists in its…
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Full text Article nitrogen cycle

From The Penguin Dictionary of Science
nitrogen cycle
A series of chemical processes, mostly occurring in organisms, in which nitrogen atoms are circulated in nature (see the diagram below). Although nitrogen is an important component of many molecules of biological significance (such as proteins, nucleic acids and chlorophyll), it can be used directly…
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Schematic representation of the various...
1 Abstract Nitrogen is one of the essential elements for all life on Earth. Various forms of inorganic nitrogen are incorporated into living cells and tissues, and subsequently recycled back into a variety of inorganic forms that sustain ocean productivity. This nitrogen cycle in the sea is driven…
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Full text Article nitrogen cycle

From The Columbia Encyclopedia
the continuous flow of nitrogen through the biosphere by the processes of nitrogen fixation, ammonification (decay), nitrification, and denitrification. Nitrogen is vital to all living matter, both plant and animal; it is an essential constituent of amino acids, which form proteins of nucleic acids…
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Full text Article Nitrogen Cycle

From Encyclopedia of Microbiology
Overview of the biological nitrogen cycle....
000 Abstract The biogeochemical nitrogen cycle (N-cycle) involves multiple redox reactions that interconvert nitrogen compounds in the biosphere. N-cycle is mainly driven by microbes that use these reactions for assimilatory, respiratory or dissimilatory purposes. Ammonium assimilation consists of…
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Full text Article nitrogen cycle and the oceans

From Science Encyclopedia: Encyclopedia of Marine Science
The continuous sequence of events by which nitrogen is converted into chemicals that can be used by plants and animals for sustaining life and building tissue is called the nitrogen cycle. The cycle is driven by uptake of nitrogen by living organisms from green plants such as phytoplankton, …
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Full text Article nitrogen cycle

From Dictionary of Microbiology & Molecular Biology
NITROGEN CYCLE—microbial aspects, with examples...
In nature: the cyclical interconversion of nitrogen and its compounds by living organisms and non-biological processes. The major microbial conversions are shown on page 522. (See also AMMONIA ASSIMILATION , AMMONIFICATION , ASSIMILATORY NITRATE REDUCTION , DENITRIFICATION , DISSIMILATORY NITRATE…
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Full text Article nitrogen cycle

From Britannica Concise Encyclopedia
Circulation of nitrogen in various forms throughout nature. Nitrogen is essential to life, but in the atmosphere it is in a form (the diatomic molecule N 2 ) unavailable to most organisms. Nitrogen fixation by microbes turns this nitrogen into nitrate s and other compounds, which plants or algae…
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