Symbiotic Nitrogen Fixation

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Symbiotic Nitrogen Fixation

	Symbiotic Nitrogen Fixation -It has been widely recognised for centuries that most crops decrease the fertility of the soil, but leguminous crops increase it. Legumes, thus restore or renew the soil. This is because legumes fix nitrogen from the air. This was first demonstrated by the French chemist Boussingault in 1837.
He observed that nitrogen present in the leguminous plants exceeded the nitrogen present in the seeds and the soil. Hellriegel and Willfarth in Germany and Atwater in USA conclusively proved that nitrogen is fixed by certain bacteria living in root nodules of the leguminous plants. Since neither the plant nor the bacterium can fix atmospheric nitrogen independently, the process, there fore, is called symbiotic nitrogen fixation.
The root nodule bacteria were later, isolated by Beijerinck in 1888 and were classified and grouped in the genus Rhizobium (Rhizo means root in Greek). These are gram negative, motile, aerobic, non sporeforming bacteria. They are, mainly rod shaped, but when isolated from nodules a variety of morphological shapes are observed.

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Sulphur Cycle Ammonification in Soil Nitrification in Soil Nitrate Reduction in Soil Denitrification in Soil Nitrogen Fixation Symbiotic Nitrogen Fixation Rhizobium Specificity of Bacteria and Legumes Non-Symbiotic Nitrogen Fixation Non-symbiotic Nitrogen Fixing Microorganisms Mechanism of Nitrogen Fixation Oxidation of Sulphur and Sulphur Compounds by Bacteria