Question

Short / Long Answer Type Questions :
What are biofertilizers? What are their main sources? What is biological nitrogen fixation? Name two organisms each which fix nitrogen asymbiotically and symbiotically.

Answer 1

A biofertilizer is a substance which contains living microorganisms which, when applied to seeds, plant surfaces, or soil, colonize the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant.The main sources of biofertilizers are bacteria, fungi, and cynobacteria (blue-green algae). Plants have a number of relationships with fungi, bacteria, and algae.

Biological nitrogen fixation (BNF) is the process whereby atmospheric nitrogen (N=N) is reduced to ammonia in the presence of nitrogenase. Nitrogenase is a biological catalyst found naturally only in certain microorganisms such as the symbiotic Rhizobium and Frankia, or the free-living Azospirillum and Azotobacter.

All the nitrogen-fixing organisms are prokaryotes (bacteria). Some of them live independently of other organisms - the so-called free-living nitrogen-fixing bacteria. Others live in intimate symbiotic associations with plants or with other organisms (e.g. protozoa).The most familiar examples of nitrogen-fixing symbioses are the root nodules of legumes. In these leguminous associations the bacteria usually are Rhizobium species, but the root nodules of soybeans, chickpea and some other legumes are formed by small-celled rhizobia termed Bradyrhizobium. Free-living aerobic bacteria of soils, such as Azotobacter and Beijerinckia.