nitrogen fixation

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ni·tro·gen fix·a·tion

process in which atmospheric nitrogen is converted to ammonia.

nitrogen fixation

n.
1. The conversion of atmospheric nitrogen into compounds, such as ammonia, by natural agencies or various industrial processes.
2. The conversion by certain soil microorganisms, such as rhizobia, of atmospheric nitrogen into compounds that plants and other organisms can assimilate.

ni′tro·gen-fix′er (-fĭk′sər) n.
ni′tro·gen-fix′ing adj.

nitrogen fixation

the process by which free nitrogen in the atmosphere is converted by biological or chemical means to ammonia and to other forms usable by plants and animals. Biological nitrogen fixation is the more important process and is accomplished by microorganisms in the soil, either free living or in close association with root nodules of certain plants. In contrast, chemical nitrogen fixation, as is used in industry, requires extremely high temperatures and pressures.

nitrogen fixation

the utilization of atmospheric nitrogen in the synthesis of AMINO ACIDS by some bacteria. Such bacteria can be free-living (e.g. Azotobacter, an aerobe; Clostridium, an obligate anaerobe) while others (e.g. Rhizobium) live in association with plants, occupying swellings in the root called root nodules. The latter relationship is one of SYMBIOSIS, in that the plant gains nutrients and thus can live in nitrogen-poor soils, while the nitrogen-fixer obtains a supply of carbohydrates from the plant. The nitrogen is reduced to ammonia in the microbes by action of the enzyme nitrogenase: N2 + 3 H22 NH3, the ammonia then reacting with keto acids to form amino acids.

nitrogen

a chemical element, atomic number 7, atomic weight 14.007, symbol N. See Table 6. It is a gas constituting about four-fifths of common air; chemically it is almost inert. It is not poisonous but is fatal if breathed alone because of oxygen deprivation. Nitrogen occurs in proteins and amino acids and is thus present in all living cells.

nitrogen balance
the state of the body in regard to the rate of protein intake and protein utilization. When protein is metabolized, about 90% of the protein nitrogen is excreted in the urine in the form of urea, uric acid, creatinine and other nitrogen end products. The remaining 10% of the nitrogen is eliminated in the feces.
A negative nitrogen balance occurs when more protein is utilized by the body than is taken in. A positive nitrogen balance implies a net gain of protein in the body. Negative nitrogen balance can be caused by such factors as malnutrition, debilitating diseases, blood loss and glucocorticoids. A positive balance can be caused by exercise, growth hormone and testosterone.
blood urea nitrogen (BUN)
see urea nitrogen.
nitrogen dioxide
see nitric oxide.
nitrogen fixation
conversion of atmospheric nitrogen into organic nitrogenous compounds by bacteria which may be symbiotic, e.g. Rhizopus spp., which grow on the roots of legumes and put those plants in an advantageous position with respect to nonlegumes.
nitrogen-free extract (NFE)
consists of carbohydrates, sugars, starches, and a major portion of the hemicellulose in feeds. Calculated when crude protein, fat, water, ash, and the fiber are added and the sum is subtracted from 100.
nitrogen mustards
a group of toxic, blistering alkylating agents homologous to dichlorodiethyl sulfide (mustard gas), some of which have been used as antineoplastics. The group includes mustine hydrochloride, cyclophosphamide, thiotepa, chlorambucil and melphalan.
nonprotein nitrogen (NPN)
1. the nitrogenous constituents of the blood exclusive of the protein bodies, consisting of the nitrogen of urea, uric acid, creatine, creatinine, amino acids, polypeptides, and an undetermined part known as rest nitrogen.
Measurement of nonprotein nitrogen is used as a test of renal function, but has been largely replaced by measurement of specific substances, e.g. urea and creatinine.
2. also used in relation to feeds and refers to those nitrogen-containing constituents which are not proteins, e.g. nucleic acids, amino sugars, urea, etc.
nitrogen trichloride
nitrogen washout test
measures the rate at which the nitrogen concentration in the expired air is reduced when the horse is made to breathe pure oxygen. The rate is less in incompetent lungs, e.g. those affected by emphysema.
References in periodicals archive ?
In our study, one nitrogen-fixing strain N1115 was obtained by re-screening with FITC-labeled rice germ lection which was showed in Fig.
Nitrogen-fixing nodules induced by Rhizobium on the stem of the tropical legume Sesbania rostrata.
Among the nitrogen-fixing organisms (or diazotrophic), many are heterotrophic, which need a reduced carbon supplement and others depend indirectly on light energy.
Azospirillum, a free-living nitrogen-fixing bacterium closely associated with grasses: genetic, biochemical and ecological aspects.
In practice, countries such as England were already importing significant quantities of nitrogen in the form of food and fiber, which meant that they were drawing on the activity of nitrogen-fixing bacteria in distant places.
His major breakthrough came when he found a specific strain of nitrogen-fixing bacteria in sugar-cane which he discovered could intracellularly colonise all major crop plants.
Nitrogen-fixing plants improve the health of the soil by drawing nitrogen from the air and transferring it to the soil through their roots and leaf litter.
Frankia are nitrogen-fixing bacteria that live symbiotically in the roots of actinorhizal plants.
In recent years various novel endophytic nitrogen-fixing bacteria have been discovered, such as Acetobacter diazotrophicus (Cavalcante and Dobereiner, 1988), Herbaspirillum seropedicae (Baldani et al.
However, their nitrogen-fixing performance varies, depending on environmental factors such as soil salinity and acidity, as well as their ability to compete with introduced rhizobia species.