What does the nitrogen cycle help maintain within ecosystems?

The nitrogen cycle is a critical biogeochemical process that helps maintain soil fertility within ecosystems. This cycle involves several key steps, including nitrogen fixation, nitrification, assimilation, ammonification, and denitrification, all of which transform nitrogen in various forms that can be utilized by plants and other organisms.

In the first step, nitrogen from the atmosphere is converted into ammonia by nitrogen-fixing organisms, making it accessible to plants. Plants then assimilate these nitrogen compounds to create essential biomolecules like proteins and nucleic acids, which are foundational for growth and development. When plants and animals die, decomposers break down their organic matter, returning nitrogen to the soil in the form of ammonium, which can be further converted into nitrates. These nitrates are reabsorbed by plants, making the nitrogen cycle a continuous loop that enhances and sustains soil fertility.

In contrast, while water clarity, temperature regulation, and population density can be influenced by various ecological factors, they are not directly maintained by the nitrogen cycle. Soil fertility, however, is directly dependent on the availability and transformative processes of nitrogen within the ecosystem, making it the most accurate choice regarding the function of the nitrogen cycle.