The main difference between nitrogen fixation and nitrification is that nitrogen fixation is the conversion of nitrogen gas (N2) into nitrogen-containing substances, whereas nitrification is the conversion of ammonium ions (NH4+) to nitrites (NO2-) and nitrates (NO3-). Furthermore, nitrogen fixation can occur through atmospheric, industrial or biological processes while nitrification is performed by soil-living bacteria and other nitrifying bacteria. Moreover, in the nitrogen cycle, nitrogen fixation is the first step, which fixes atmospheric nitrogen into ammonium ions while nitrification is the next step in which ammonium ions are converted into nitrites.
Nitrogen fixation and nitrification are two processes of the nitrogen cycle.
Key Areas Covered
1. What is Nitrogen Fixation
– Definition, Process, Importance
2. What is Nitrification
– Definition, Process, Importance
3. What are the Similarities Between Nitrogen Fixation and Nitrification
– Outline of Common Features
4. What is the Difference Between Nitrogen Fixation and Nitrification
– Comparison of Key Differences
Key Terms
Ammonium Ions, Atmospheric Nitrogen, Nitrates, Nitrites, Nitrification, Nitrogen Fixation
What is Nitrogen Fixation
Nitrogen fixation is the first step of the nitrogen cycle, and it converts atmospheric nitrogen into ammonium ions. Generally, 80% of the earth’s atmosphere contains nitrogen gas. Still, nitrogen is a limiting nutrient factor for primary producers as they are unable to assimilate atmospheric nitrogen. Therefore, the nitrogen cycle is responsible for the conversion of the atmospheric nitrogen into the nitrogen substances, which can be readily absorbed by primary producers.
Figure 1: Nitrogen Cycle
Furthermore, in the nitrogen cycle, both free-living organisms, as well as the symbiotic organisms, undergo the fixation of nitrogen. Significantly, all of these nitrogen-fixing organisms share a similar feature, which is that all of them have the same enzyme complex, nitrogenase. Also, this enzyme complex catalyzes the reduction of nitrogen gas into ammonia (NH3).
Additionally, the examples of free-living nitrogen-fixing bacteria that are aerobic include Pseudomonas, Azotobacter, Methylomonas, Alcaligenes, and Thiobacillus. Also, Nostoc and Anabaena are free-living cyanobacteria that are aerobic, fixing nitrogen. On the other hand, the free-living, anaerobic organisms that fix nitrogen include Methanosarcina, Methanococcus, Charomatium, Chlorobium, Desulfovibrio, and Clostridium. Moreover, Rhizobium and Frankia are the symbiotic bacteria that live in the root nodules of legumes, fixing nitrogen.
Although the nitrogen cycle is the biological process of nitrogen fixation, the Haber-Bosch process is the method of nitrogen fixation in the industry. Also, atmospheric fixation of nitrogen is the third method of nitrogen fixation in which the enormous energy of lightning breaks nitrogen molecules, enabling their atoms to combine with oxygen to form nitrogen oxide. However, these nitrogen oxides dissolve in the rain, forming nitrates carried to the earth.
What is Nitrification
Nitrification is the second step of the nitrogen cycle, converting ammonium ions into nitrites and nitrates. Significantly, bacteria carry out nitrification. However, this process occurs in two consequent substeps carried out by different bacteria. The first substep is the conversion of ammonia into nitrites, and the second substep is the conversion of nitrites into nitrates. Here, the first substep is the oxidation of ammonia into nitrites. Also, aerobic ammonia-oxidizers such as Nitrosomonas, Nitrosospira, and Nitrosococcus carry out this first substep. Foremost, ammonia monooxygenase converts ammonia into hydroxylamine, which is then converted into nitrite by the action of the enzyme, hydroxylamine oxidoreductase.
Figure 2: Chemical Reaction of the Nitrogen Cycle
Moreover, the second substep is the oxidation of nitrites into nitrates. Also, a separate group of nitrogen-oxidizing bacteria, including Nitrospira, Nitrobacter, Nitrococcus, and Nitrospina carry out this substep. Additionally, the enzyme responsible for the oxidization of nitrites into nitrates is nitrite oxidoreductase. For instance, both ammonia oxidizers and nitrite oxidizers are ubiquitous in aerobic habitats, including soils, estuaries, lakes, and open-ocean environments. Also, they play a key role in wastewater treatment facilities, removing harmful levels of ammonium. In the meanwhile, ammonia-oxidizing Archaea are abundant in oceans, soils, and salt marshes. One of the ammonia-oxidizing archaeon grown in pure culture is Nitrosopumilus maritimus.
Similarities Between Nitrogen Fixation and Nitrification
- Nitrogen fixation and nitrification are two steps of the nitrogen cycle.
- They are responsible for the conversion of the atmospheric nitrogen into substances, which can be used by organisms.
- Soil bacteria undergo both processes.
Difference Between Nitrogen Fixation and Nitrification
Definition
Nitrogen fixation refers to the chemical processes of the nitrogen cycle that assimilate atmospheric nitrogen into the organic compounds, especially by certain microorganisms. On the other hand, nitrification refers to the biological oxidation of ammonia or ammonium to nitrite followed by the oxidation of the nitrite to nitrate.
Significance
Nitrogen fixation is the conversion of nitrogen gas into ammonia while nitrification is the conversion of ammonium to nitrites and nitrates.
Type of Process
Nitrogen fixation can occur through atmospheric, industrial or biological processes while nitrification is performed by soil-living bacteria and other nitrifying bacteria.
In the Nitrogen Cycle
Nitrogen fixation is the first step, which fixes atmospheric nitrogen into ammonium ions while nitrification is the next step in which ammonium ions are converted into nitrites.
Microorganisms
Nitrogen-fixing soil bacteria such as Cyanobacteria and the bacteria living in root nodules such as Rhizobium are responsible for nitrogen fixation while nitrifying bacteria such as Nitrosomonas and Nitrobacter are responsible for the nitrification.
Conclusion
Nitrogen fixation is the process of converting atmospheric nitrogen into the nitrogen substances, which can be taken up by plants. Therefore, in the nitrogen cycle, atmospheric nitrogen converts into ammonium ions. Also, soil bacteria, including cyanobacteria and the symbiotic bacteria in the root nodules, including Rhizobium, undergo nitrogen fixation. On the other hand, nitrification is the second step of the nitrogen cycle, converting ammonium ions into nitrites and nitrates. Also, Nitrosomonas and Nitrobacter are the two types of nitrifying bacteria responsible for the nitrification. Hence, the main difference between nitrogen fixation and nitrification is the type of conversion and types of microorganisms involved in the process.
References:
1. Bernhard, Anne. “The Nitrogen Cycle: Processes, Players, and Human Impact.” Nature News, Nature Publishing Group, Available Here.
Image Courtesy:
1. “Nitrogen Cycle 2” By File:Nitrogen Cycle.svg (CC BY-SA 3.0) via Commons Wikimedia
2. “Table of the Processes in the Nitrogen Cycle” By Holivi5 – Own work (CC BY-SA 4.0) via Commons Wikimedia
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