Which process helps to complete the nitrogen cycle by converting ammonia back into nitrogen gas?

The process that correctly completes the nitrogen cycle by converting ammonia back into nitrogen gas is denitrification. This is a crucial step in the nitrogen cycle, where certain bacteria in the soil utilize nitrate as an energy source and convert it into nitrogen gas, which is then released into the atmosphere. This process helps to balance the nitrogen concentration in ecosystems and plays a vital role in reducing the excess nitrogen that might accumulate from other processes, such as fertilization.

In more detail, denitrification typically occurs under anaerobic (low oxygen) conditions, where denitrifying bacteria, such as Pseudomonas and Paracoccus species, thrive. These bacteria convert nitrates (NO3-) produced from nitrification or other processes back into nitrogen gas (N2), effectively closing the loop of the nitrogen cycle.

Understanding this process helps emphasize the importance of microbial activity in maintaining nitrogen balance within ecosystems, highlighting how natural processes can regulate nutrient cycling and sustain plant growth.