Which process transforms nitrogen gas into ammonia or nitrate?

The process that transforms nitrogen gas into ammonia or nitrate is known as nitrogen fixation. This process is crucial for converting atmospheric nitrogen, which most organisms cannot utilize, into forms that can be assimilated by living organisms, such as ammonia (NH3) and nitrate (NO3-).

Nitrogen fixation occurs primarily through two pathways: biological fixation, which is carried out by specific bacteria and archaea, including those found in the root nodules of leguminous plants, and abiotic fixation, which includes processes such as lightning or industrial methods. This conversion is fundamental because nitrogen is an essential nutrient for plant growth, influencing overall ecosystem productivity.

In contrast, while nitrification involves the conversion of ammonia into nitrites and then into nitrates, and denitrification refers to the process by which nitrates are reduced back to nitrogen gas, they do not initiate the transformation from atmospheric nitrogen. Decomposition is related to the breakdown of organic matter and does not directly relate to the transformation of nitrogen gas. Thus, nitrogen fixation accurately describes the process of converting nitrogen gas into usable forms like ammonia and nitrate.