Which term describes the process where bacteria return nitrogen to the atmosphere?

Denitrification is the process through which bacteria convert nitrates and nitrites in the soil back into nitrogen gas (N₂), which is then released into the atmosphere. This process is crucial in the nitrogen cycle as it helps maintain the balance of nitrogen in the environment.

During denitrification, specific bacteria, often found in anaerobic conditions (where oxygen is limited), convert these nitrogen compounds back into atmospheric nitrogen. This not only reduces the nitrogen levels in the soil, helping to prevent nutrient overload in ecosystems but also facilitates the recycling of nutrients, allowing for a sustainable nitrogen cycle.

In contrast, assimilation involves the uptake of nitrogen by plants and other organisms. Nitrification is the microbial conversion of ammonia to nitrates, which plants can use, and fixation refers to the process where atmospheric nitrogen is converted into a form usable by living organisms, typically through the actions of certain bacteria. Each of these processes plays a unique role in the nitrogen cycle, but denitrification specifically addresses the return of nitrogen to the atmosphere.