What organism primarily utilizes the nitrogen from the atmosphere?

Nitrogen-fixing bacteria play a crucial role in the nitrogen cycle by converting atmospheric nitrogen (N₂) into forms that are usable by living organisms. Although atmospheric nitrogen is abundant, most organisms cannot utilize it directly. Nitrogen-fixing bacteria, such as those in the genera Rhizobium and Azotobacter, have specialized enzymes that allow them to convert nitrogen gas into ammonia (NH₃) or related compounds, which can then be taken up by plants.

This process is vital for the ecosystem because it makes nitrogen accessible to plants, which are primary producers in most ecosystems. Once plants absorb the nitrogen, it enters the food web as herbivores consume the plants and carnivores consume the herbivores, effectively transferring the nitrogen up the trophic levels. Consequently, without nitrogen-fixing bacteria, the supply of usable nitrogen would diminish, severely impacting plant growth and the entire food chain.

Understanding this relationship highlights the foundational role of nitrogen-fixing bacteria in promoting soil fertility, ecosystem productivity, and overall environmental health.