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Saturday, July 18, 2009

Sesbania sp. : The Great Nitrogen Fixer

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The leguminous plants such as clover, beans, alfalfa, lupines, and peanuts need plenty of nitrogen but they don't have a technology to stop and capture the nitrogen of air. Neither can they capture plenty of nitrates from the surrounding. But they are clever enough to take help from the Rhizobia (singular- Rhizobium) and a few other bacteria that are technologically more advanced in this work. For this, the leguminous plants have to make special nodules in their roots as homes for their habilitation. These bacteria convert the nitrogen of air into inorganic compounds of nitrogen (for example: Ammonium) and offer the same to the plant of whom they are guests. Now, plants can utilize this compound to assimilate amino acids which is essential for the formation of proteins. This much portion of the nitrogen cycle is called as Biological Nitrogen Fixation. Not all the leguminous plants have bacterial associations for fixing nitrogen. Styphnolobium is one example.


Many non-leguminous plants also fix nitrogen. Such plants are called as actinorhizal plants. These comprise many shrubs and woody trees. Some plants of birch family like Alder (Alnus); Mountain Mahogany; Cliff- rose; Dryas etc are examples of such plants. The bacteria or other microorganisms that fix nitrogen are called as Diazotrophs.

The Biological Nitrogen Fixation was first discovered by a Dutch Microbiologist Martinus Beijerinck.The stems of some plants like Sesbania Plant too, have nodules on them. Do you think that all the nitrogen fixed by nodules on a particular plant is used by the same plant alone? No, the remaining nitrogen is spent in improving the fertility of soil.

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