I. Interpretation
Nitrogen fixation refers to the process of transforming free nitrogen in the air into nitrogen-containing compounds. This transformation can be carried out by natural or artificial means. For example, leguminous plants and rhizobia can absorb nitrogen molecules in the atmosphere and convert them into ammonia and ammonium ions, which is a natural nitrogen fixation.
Second, the role of nitrogen fixation
Nitrogen fixation is the process of transforming free nitrogen in the air into nitrogen-containing compounds, which is of great significance to the growth and development of plants. Plants can absorb these nitrogenous compounds to synthesize biomacromolecules such as protein and nucleic acid, which can promote the growth and development of plants.
Nitrogen fixation also provides food sources for animals. A large number of nitrogen-containing compounds synthesized by plants by absorbing nitrogen in the atmosphere will be further utilized by animals to synthesize their own tissues and organs, thus providing an important source of nutrition for the survival of animals.
How does nitrogen fixation work?
First of all, lightning
With its great energy, lightning dissociates nitrogen molecules in the atmosphere, and continues to react with oxygen molecules to generate nitrogen oxides, which will dissolve in rainwater to generate nitrite and nitrate, and penetrate into the soil.
Although lightning often occurs all over the world, lightning nitrogen fixation is not an effective method to produce nitrogen-containing compounds. Nitrogen compounds obtained by lightning nitrogen fixation only account for 10% of the annual total.
Second, nitrogen-fixing bacteria
This is the most important nitrogen fixation method, which needs the help of some nitrogen-fixing bacteria, such as rhizobia, which exist in soil alone or with animals and plants and have nitrogen-fixing enzymes.
They can absorb nitrogen molecules in the atmosphere and convert them into ammonia and ammonium ions. Every year, nitrogen-containing compounds obtained by bacterial nitrogen fixation account for about 65% of the total. Some plants also have the ability to fix nitrogen, such as beans and grasses. These plants can transform nitrogen in the atmosphere into nitrogen-containing compounds through symbiosis with nitrogen-fixing bacteria or the action of their own nitrogen-fixing enzymes.