Non-symbiotic Nitrogen Fixation

Around 80% of the atmosphere comprises nitrogen gas. But plants cannot access the nitrogen in the air. There are specific bacteria that turn atmospheric nitrogen into ammonia so that it can be used by plants. Free-living (nonsymbiotic) and non-free-living (symbiotic) bacteria are both capable of fixing nitrogen.

  • Cyanobacteria, Azotobacter, and Clostridium are a few examples of non-symbiotic or free-living bacteria.
  • Bacteria that are symbiotic include Bradyrhizobium and Rhizobium.

Here, let’s learn more about the process of non-symbiotic nitrogen fixation.

Table of Contents

Non-symbiotic Nitrogen Fixation

Soil microorganisms are responsible for around 90% of the biotic nitrogen fixation that happens naturally on our planet. Examples of abiotic or non-biological natural inducers include UV radiation and lightning. Additionally, nitrogen can be fixed industrially or with electrical equipment. The two types of biotic or biological nitrogen fixation are – non-symbiotic and symbiotic nitrogen fixation.

The fixation of atmospheric nitrogen by soil bacteria that are free-living is known as non-symbiotic nitrogen fixation. One of the non-symbiotic anaerobic bacteria that fixes nitrogen is Clostridium pasteurianum. Azotobacter chroococcum is another aerobic, free-living bacteria that fix atmospheric nitrogen. Azotobacter and Beijerinckia are the two major bacterial species engaged in nitrogen fixation in tropical climate regions, which supply nutrients for the growth of numerous crops.

Steps

Ammonia production and nitrification are the two main processes involved in non-symbiotic nitrogen fixation.

  1. By the reduction of nitrogen in the atmosphere, ammonia is created. Nitrosomonas, Nitrosococcus, and Nitrosospira turn ammonia into nitrite.

NH3– (Ammonia) →NO2– (Nitrite)

  1. When ammonia is converted to nitrite and nitrate, nitrifying bacteria play a major role. Nitrobacter, Nitrospina, Nitrococcus, and Nitrospira then change nitrite into nitrate.

NO2– -(Nitrite) →NO3– (Nitrate)

What is denitrification?

The process of denitrification involves turning nitrate (NO3– ) into gaseous nitrogen (N2) in order to release the nitrogen component back into the atmosphere.

Non-symbiotic nitrogen fixation

Also Check:Nitrogen Cycle

Non-symbiotic Nitrogen Fixing Bacteria

Non-symbiotic nitrogen-fixing bacteria are quite primitive. The fixation is a reducing process that is separate from respiration. Under poor aeration, these organisms fix nitrogen more actively, provided no hydrogen gas is being generated. Here are some examples of such non-symbiotic nitrogen-fixing bacteria:

  • Aerobic – Chlorobium and Chromatium (Photosynthetic), Beijerinckia and Azotobacter (Non-photosynthetic)
  • Anaerobic – Rhodospirillum (Photosynthetic) and Clostridium (Non-photosynthetic)
  • Blue-green algae – Nostoc, Anabaena, Oscillatoria, etc.
  • Chemosynthetic – Desulfovibrio

Nitrogen Fixation

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Frequently Asked Questions

Q1

What is the nitrogen cycle?

The nitrogen cycle is a cyclic process that transforms inert nitrogen from the atmosphere into a form of nitrogen that is more useful to living things. This cycle is prevalent in both marine and terrestrial ecosystems and is crucial for maintaining a correct ecological equilibrium.
Q2

What is asymbiotic nitrogen fixation?

Asymbiotic or non-symbiotic nitrogen fixation refers to biological nitrogen fixation by microorganisms that are free to move about or remain outside of plant cells. Example – Azotobacter and Rhodospirillum.
Q3

What is the difference between non-symbiotic and symbiotic nitrogen fixation?

The major distinction between symbiotic and non-symbiotic nitrogen fixation is that the former is a result of nitrogen-fixing bacteria that coexist symbiotically with the host plant, whilst the latter is a result of free-living bacteria in the soil.
Q4

What are some advantages of nitrogen fixation?

Nitrogen fixation boosts nitrogen content in soil without the use of fertilisers. Some can also fix nitrogen in leguminous plant root nodules.
Q5

How do legume plants aid in the fixing of nitrogen?

Rhizobia, a type of soil bacteria that fixes nitrogen, can coexist symbiotically with legumes. This symbiosis causes nodules to grow on the plant roots, where the bacteria may transform atmospheric nitrogen into plant-useable compounds.