What process involves the assimilation of atmospheric nitrogen by soil bacteria for plant use?

Nitrogen fixation is the process in which atmospheric nitrogen (N₂) is converted into a form that is usable by plants, specifically into ammonia (NH₃) or related compounds. This process is carried out by certain types of soil bacteria, often referred to as nitrogen-fixing bacteria, which possess the unique ability to convert inert nitrogen gas from the atmosphere into biologically usable forms.

These bacteria either live freely in the soil or in symbiotic relationships with the roots of specific plants, such as legumes. When plants take up the fixed nitrogen, they can then utilize it to produce essential biomolecules like amino acids and nucleic acids, which are vital for growth and development. Nitrogen fixation is a crucial step in the nitrogen cycle, as it makes atmospheric nitrogen available in a form that can be assimilated by living organisms, thus playing a fundamental role in ecosystem productivity.

The other processes mentioned involve different aspects of nitrogen cycling, such as transforming nitrates back into nitrogen gas or converting organic matter into ammonium, but they do not specifically relate to the initial conversion of atmospheric nitrogen into a form usable by plants.