nitrogen cycle

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ni·tro·gen cy·cle

the series of events in which the nitrogen of the atmosphere is fixed, thus made available for plant and animal life, and is then returned to the atmosphere: nitrifying bacteria convert N2 and O2 to NO2- and NO3-, the latter being absorbed by plants and converted to protein; if plants decay, the nitrogen is in part given up to the atmosphere and the remainder is converted by microorganisms to ammonia, nitrites, and nitrates; if the plants are eaten, the animals' excreta or bacterial decay return the nitrogen to the soil and air.

nitrogen cycle

n.
The circulation of nitrogen in nature, consisting of a cycle of chemical reactions in which nitrogen from the atmosphere is fixed in compounds in soil or water, assimilated by plants and animals, released to the soil and water through decomposition, and returned to the atmosphere through denitrification.

nitrogen cycle

Etymology: Gk, nitron, soda, genein, to produce, kyklos, circle
the circulation of nitrogen through natural processes in either of two ways: from the soil to organisms that excrete nitrogen products back into the soil or by bacterial fixation of atmospheric nitrogen through other organisms that decay and release the element back into the atmosphere.

ni·tro·gen cy·cle

(nī'trŏ-jĕn sī'kĕl)
The series of events in which the nitrogen of the atmosphere is fixed, thus made available for plant and animal life, and is then returned to the atmosphere: nitrifying bacteria convert N2 and O2 to NO2- and NO3-, the latter being absorbed by plants and converted to protein; if plants decay, the nitrogen is in part given up to the atmosphere and the remainder is converted by microorganisms to ammonia, nitrites, and nitrates; if the plants are eaten, the animals' excreta or bacterial decay return the nitrogen to the soil and air.
Nitrogen cycleclick for a larger image
Fig. 229 Nitrogen cycle .

nitrogen cycle

the circulation of nitrogen in the environment as a result of the activity of living organisms. 80% of the atmosphere is made up of nitrogen and this is maintained by the balancing action of the cycle.