Hello aspirant,
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Examples of Nitrogen Fixers -

1. Free living Nitrogen Fixers -

Aerobic - Azotobacter, Beijerinckia
Anaerobic - Clostridium, Rhodospirillum

2. Symbiotic Nitrogen Fixers -

Rhizobium (unicellular, heterotrophic, associated with leguminous plants like alfalfa, sweet clover, sweet pea, lentils, garden pea, broad bean, clover bean)

Frankia (filamentous, heterotrophic, associated with non leguminous plants like Alnus)

Anabaena (filamentous, autotrophic, associated with non leguminous plants)


Note -
Rhizobium, Frankia and Anabaena are free living in soil, but as symbionts, can fix atmospheric nitrogen.

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Best Of Luck