Assimilation of Atmospheric Nitrogen

Assimilation of Atmospheric Nitrogen. — It is especially to the French scientists that agricultural bacteriology owes its 

The moist soils on which molds and algae grow are rich in nitrogen. This assimilation, as Kossowicz has plainly shown by means of a pure culture of Chorella vulgaris, results from a work of symbiosis which takes place between these lower plants 

The quantity of nitrogen assimilated by the algae and the molds is ordinarily considered as being too small to be taken into account. Only bacteria are of real interest from the point of view of the enrichment of the soil in combined nitrogen. And yet, of all these, the most important, as we shall see, are those which are capable of living in symbiosis with the plant. 

From the earliest times, it has been noted that certain crops, such as those of leguminous plants, improve the soil, and that others, like those of cereals, exhaust it. This observation for a long time served as the basis of agriculture, before the exact cause was known. More recent studies have revealed that the mechanism of this enrichment is due to an assimilation of nitrogen, an assimilation originating in the radicular nodules 

The catalysts that intervene in the assimilation of nitrogen by micro-organisms are unknown. They form a field of investigation still unexplored. However, it has been established that enzymes play a considerable part in the symbiosis of bacteria with plants. The bacterium is attached to the plant by means of active substances, and it is by means of the secretions of the radicular system that the utilization of the nitrogenous reserve of bacterial origin takes place. 

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The volcanic nitrogen found was attributed in the older literature to mixing with air (which is not likely because of missing argon) and decomposition of organic nitrogen from deposits into the crater (Bischof 1863). Today it is believed that all ammonia/ammonium (Sutton et al. 2008) on earth is the result of biological activity, i.e., by assimilation of atmospheric N2 and subsequent nitrification into NH3. 

Assimilation of nitrogen by land plants (106 t/yr) From the atmosphere From the soil 30 5.3... 

Nitrate reduction studies have focused overwhelmingly on denitrification at the expense of other NO sinks such as dissimulatory NO reduction to NH4 (also known as DNRA or nitrate ammonification). The ecological implications of reducing NOJ to NH4, versus N2 are vastly different because NH4 is more readily retained in the ecosystem, and it is a form that is readily assimilated by biota. Thus, DNRA contributes to eutrophication by reducing the quantity of fixed nitrogen that is returned to the atmosphere as N2. 

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