Nitrogen-fixing microorganisms include autotrophic and heterotrophic. Nitrogen-fixing microorganisms are a kind of organisms that can fix nitrogen in the atmosphere. They play a key role in the natural nitrogen cycle. The metabolic types of these microorganisms are diverse, including autotrophic and heterotrophic. Autotrophic nitrogen-fixing microorganisms can use carbon dioxide and inorganic substances to synthesize organic matter, while heterotrophic nitrogen-fixing microorganisms need organic carbon compounds as carbon sources and energy sources. Nitrogen-fixing microorganisms refer to microorganisms that directly convert free nitrogen in the air into nitrogen-containing compounds through life activities. There are many kinds of nitrogen-fixing microorganisms, which can be divided into aerobic autotrophic nitrogen-fixing microorganisms, anaerobic autotrophic nitrogen-fixing microorganisms and autotrophic nitrogen-fixing microorganisms.