Concept:Nutrient cycling involves the movement and recycling of essential elements through living and non-living parts of an ecosystem.
Explanation:Nutrient cycling is driven by processes that convert nutrients into forms organisms can use and then return them to the environment.
Nitrogen fixation converts atmospheric nitrogen gas (
N2) into ammonia/ammonium (
NH4+) usable by plants.
Denitrification returns nitrates to nitrogen gas, completing the nitrogen cycle.
Ammonification releases ammonium from dead organic matter through decomposition.
Together, these processes describe the nitrogen cycle, a major nutrient cycle in ecosystems.
The other options describe geological changes, aspects of the water cycle, or energy-related processes, not direct nutrient cycling.
Answer:C. Nitrogen fixation, denitrification, and ammonification