What process do nitrifying bacteria facilitate in the nitrogen cycle?

Nitrifying bacteria play a crucial role in the nitrogen cycle by facilitating the conversion of ammonium into nitrites and then into nitrates. This two-step process is essential for preparing nitrogen compounds that plants can easily absorb and use for growth.

Initially, these bacteria oxidize ammonium (NH4+) into nitrites (NO2-), and then other types of nitrifying bacteria further oxidize the nitrites into nitrates (NO3-). Nitrates are particularly important in the nitrogen cycle as they are the forms of nitrogen most readily taken up by plants. This conversion process not only helps in making nitrogen available to plant life but also assists in regulating nitrogen levels in the soil, preventing the accumulation of harmful substances.

Other options address different aspects of the nitrogen cycle but do not describe the specific actions of nitrifying bacteria. For example, converting atmospheric nitrogen into ammonia is the role of nitrogen-fixing bacteria, while breaking down organic matter into nitrogen involves different microbial processes. Reducing nitrates back to atmospheric nitrogen is the function of denitrifying bacteria, which is separate from the nitrification process. Therefore, option B accurately encapsulates the particular role of nitrifying bacteria in the nitrogen cycle.