Biological Nitrogen Fixation
Biological nitrogen fixation refers to the process in which molecular nitrogen in the atmosphere is reduced to ammonia by nitrogenase in the body of microorganisms (nitrogen-fixing organisms). It is one of the important sources of soil nitrogen.
According to the characteristics of nitrogen-fixing microorganisms and their relationship with other organisms, they are generally divided into three types: symbiotic nitrogen fixation, autogenous nitrogen fixation, and associative nitrogen fixation.
Symbiotic nitrogen fixation mainly refers to legume – rhizobium system, other non-legume – actinomycetes nitrogen fixation system, and duckweed – cyanobacteria nitrogen fixation system.
Autogenic nitrogen fixation refers to a class of microorganisms that can fix nitrogen independently without symbiosis with other organisms, such as nitrogen-fixing bacteria and nitrogen-fixing cyanobacteria, including autotrophic and heterotrophic nitrogen fixation.
Associative nitrogen fixation system is composed of bacteria with nitrogen-fixing ability that gather around the root system of the plant and even partially enter the root cell. The existence of associative nitrogen fixation system has been confirmed in wheat, rice, and sorghum.
Biological nitrogen fixation is more suitable for neutral or slightly alkaline environments, and phosphorus fertilizers can promote symbiotic nitrogen fixation. Symbiotic nitrogen fixation is the most important.
Roadmap for Biological Nitrogen Fixation
Biological nitrogen fixation can provide crops with nitrogen needed for growth. Relying on nitrogen-fixing bacteria, the nitrogen utilization rate can reach 100%, and the global biological nitrogen fixation can reach 200 million tons per year, which exceeds the total production of industrial nitrogen fertilizers, and has great application potential in agricultural production.
Nitrogen is an indispensable nutrient element for plant growth and the main source of protein synthesis. Nitrogen-fixing bacteria are good at taking nitrogen from the air. They can convert the nitrogen in the air into nitrogen fertilizer, which can be continuously absorbed by plants.
Of all nitrogen-fixing bacteria, the most important is Rhizobium.
Rhizobium usually lives in the soil and feeds on animal and plant residues. When the corresponding legume grows in the soil, the rhizobia quickly moves towards its root and enters the root from the bend of the root hair.
Under the stimulation of rhizobia, the root cells of leguminous plants accelerate their division and enlargement, forming large and small “nodules”, which provide an ideal place for rhizobia to operate, and also provide abundant nutrients for the growth and reproduction of rhizobia.
Rhizobia will absorb nitrogen from the air, and produce “nitrogen fertilizers” for legumes to keep them thriving. In this way, the rhizobia form a symbiotic relationship with the legumes, and the nodules are often called symbiotic nitrogen-fixing bacteria. The nitrogen fertilizer produced by rhizobia can not only meet the needs of legumes, but also can provide some to help surrounding crops and store some for the next crop.
At present, the chemical method used by humans to produce nitrogen fertilizer not only requires very harsh conditions such as high temperature and high pressure, but also wastes a lot of raw materials, and the effective utilization rate of nitrogen molecules is very low. Nitrogen-fixing bacteria fix about 150 million tons of nitrogen fertilizer from the air each year. The amount of biological nitrogen fixation is three times that of the total amount of chemical nitrogen fertilizer produced in the world.
Reference
- Applications of Nitrogen-Fixing Cyanobacteria In Agriculture
- Application of Paenibacillus Mucilaginosus & Bradyrhizobium Japonicum in Agriculture
- The Symbiotic Mechanism of Bradyrhizobium and Peanut
- The Role of Rhizobia in Contaminated Soil Remediation
- Interactions Between Arbuscular Mycorrhizal Fungi, Rhizobia & Phosphate-solubilizing Bacteria