Which organisms are involved in nitrogen fixation?

The process of nitrogen fixation is primarily carried out by specific organisms that can convert atmospheric nitrogen gas (N₂) into forms usable by living organisms, such as ammonia (NH₃). This is a crucial ecological process because most organisms cannot use atmospheric nitrogen directly.

Bacteria, particularly certain soil bacteria and cyanobacteria, are the key players in nitrogen fixation. Species such as Rhizobium, which form symbiotic relationships with the roots of leguminous plants, and free-living bacteria like Azotobacter and Clostridium, possess the enzymes necessary to break the strong triple bond in molecular nitrogen, thereby making it accessible in a form that plants can utilize. Cyanobacteria, which are photosynthetic bacteria found in aquatic environments and some soil, also have the capability of fixing nitrogen through specialized cells called heterocysts.

In contrast, legumes, while important in nitrogen-fixing symbiosis, do not exclusively carry out the nitrogen fixation process on their own; they rely on the bacteria associated with them. Other choices include organisms that either do not have the ability to fix nitrogen or are too broad in their classification, as not all soil bacteria contribute to nitrogen fixation. Thus, the involvement of cyanobacteria and certain soil bacteria specifically makes this