Difference Between Symbiotic and Non Symbiotic Nitrogen Fixation

The main difference between symbiotic and non symbiotic nitrogen fixation is that the symbiotic nitrogen fixation is a function of nitrogen-fixing bacteria that live in symbiotic relationships with the host pants whereas the non symbiotic nitrogen fixation is a function of free-living bacteria in the soil.

Symbiotic and non-symbiotic nitrogen fixation are two types of biological nitrogen fixation methods carried out by bacteria.

Key Areas Covered

1. What is Symbiotic Nitrogen Fixation
     – Definition, Facts, Examples of Bacteria
2. What is Non Symbiotic Nitrogen Fixation
     – Definition, Facts, Examples of Bacteria
3. What are the Similarities Between Symbiotic and Non Symbiotic Nitrogen Fixation
     – Outline of Common Features
4. What is the Difference Between Symbiotic and Non Symbiotic Nitrogen Fixation
     – Comparison of Key Differences

Key Terms

Free-Living Bacteria, Non Symbiotic Nitrogen Fixation, Symbiotic Bacteria, Symbiotic Nitrogen Fixation

What is Symbiotic Nitrogen Fixation

Symbiotic nitrogen fixation is the fixation of atmospheric nitrogen by symbiotic bacteria that live in the root nodules. These bacteria maintain mutually beneficial relationships with plants such as legumes, pod-bearing plants such as peas, beans, alfalfa and clovers. The fixed nitrogen can be used by the next generation of legumes in the same soil.

Figure 1: Symbiosis in Root Nodules

Symbiotic bacteria first infect the root hairs, forming sheathes-like invagination. The proliferation of the nearby root cells is induced due to the production of auxin by bacteria. This forms the root nodules. Then, the bacteria produce meta-hemoglobin, which traps oxygen in order to maintain anaerobic conditions required by the fixation of the nitrogen gas. Nitrogenase is the enzyme involved in the nitrogen fixation reaction, decreasing the activation energy of the reduction reaction of N₂ into ammonia/NH₃. This ammonia is then transformed into organic compounds such as amino acids.

What is Non Symbiotic Nitrogen Fixation

Non-symbiotic nitrogen fixation is the fixation of atmospheric nitrogen by the bacteria that are free-living in the soil. Clostridium pasteurianum is one of the anaerobic bacterium, which is a non-symbiotic nitrogen-fixing bacteria. Another free-living, aerobic bacterium that fix atmospheric nitrogen is Azotobacter chroococcum. Granulobacter is a group of bacteria that can obtain nitrogen directly from the atmosphere. In tropical climate regions, Azotobacter and Beijerinckia are the main bacterial species involved in nitrogen fixation, providing nutrients for the growth of many crops.

Figure 2: Role of Two Types of Nitrogen-Fixing Bacteria

The two main steps of non-symbiotic nitrogen fixation are formation of ammonia and nitrification. Ammonia is formed by reducing the atmospheric nitrogen. Then, nitrifying bacteria help in the conversion of ammonia into nitrite and nitrate. Ammonia is converted into nitrite by Nitrosomonas, Nitrosococcus, and Nitrosospira. Then, nitrite is converted into nitrate by Nitrobacter, Nitrospina, Nitrococcus, and Nitrospira.

Similarities Between Symbiotic and Non Symbiotic Nitrogen Fixation

• Symbiotic and non symbiotic nitrogen fixation are two types of biological nitrogen-fixing processes.
• Both have the ability to convert atmospheric nitrogen into soluble nitrogen compounds such as amino acids, nitrates, nitrites, and ammonia.

Difference Between Symbiotic and Non Symbiotic Nitrogen Fixation

Definition

The symbiotic nitrogen fixation refers to a part of a mutualistic relationship in which plants provide a niche and fixed carbon to bacteria in exchange for fixed nitrogen while the non symbiotic nitrogen fixation refers to a process of biological nitrogen fixation performed by a group of autotrophic bacteria living free in the soil either aerobically or anaerobically and not dependent on plants.

Bacterial Habitat

Symbiotic nitrogen fixation bacteria live in a mutualistic relationship with plants while non-symbiotic nitrogen fixation bacteria are free-living in the soil.

Forming Nitrogen Compounds

Ammonia, amino acids, and ureides are formed during symbiotic nitrogen fixation while ammonia, nitrites, and nitrates are formed during the non-symbiotic nitrogen fixation.

Supplement

The symbiotic bacteria produce nitrogen for its host while non-symbiotic bacteria make nitrogen available in the soil.

Examples

Some nitrogen-fixing bacteria are Rhizobium meliloti, Rhizobium trifolii, Rhizobium leguminosarum, etc. while non-symbiotic nitrogen-fixing bacteria are Azotobacter spp., Beijerinckia, Granulobacter, etc.

Conclusion

Symbiotic nitrogen fixation is the fixation of nitrogen by symbiotic bacteria that live in mutualistic relationships with plants while non symbiotic nitrogen fixation is the fixation of nitrogen by free-living, soil bacteria. The main difference between symbiotic nitrogen fixation and non symbiotic nitrogen fixation is the type of nitrogen-fixing bacteria involved in each process.

Reference:

1. Shreeja D. “Symbiotic and Non-Symbiotic Nitrogen Fixing Bacteria.” Soil Management India, 20 July 2016, Available Here

Image Courtesy:

1. “Symbiosis in Root Nodules” By Joyline Chepkorir – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Nitrogen Cycle” By Cicle_del_nitrogen_de.svg: *Cicle_del_nitrogen_ca.svg: Johann Dréo (User:Nojhan), traduction de Joanjoc d’après Image:Cycle azote fr.svg.derivative work: Burkhard (talk)Nitrogen_Cycle.jpg: Environmental Protection Agencyderivative work: Raeky (talk) – Cicle_del_nitrogen_de.svgNitrogen_Cycle.jpg (CC BY-SA 3.0) via Commons Wikimedia