Nitrogen cycle

Definition

The nitrogen cycle is the biogeochemical process through which nitrogen is converted between its various chemical forms, enabling it to be used by living organisms. This cycle involves several key processes including nitrogen fixation, nitrification, denitrification, and ammonification, connecting various Earth's spheres and influencing ecosystem dynamics.

5 Must Know Facts For Your Next Test

1. Nitrogen makes up about 78% of Earth's atmosphere but is largely unavailable to most organisms until converted through biological processes.
2. The majority of nitrogen fixation in terrestrial ecosystems is performed by symbiotic bacteria associated with leguminous plants.
3. Ammonification, or mineralization, occurs when organic nitrogen from dead organisms is converted back into ammonia by decomposers.
4. Human activities, such as the use of synthetic fertilizers and fossil fuel combustion, have significantly altered the natural nitrogen cycle, leading to environmental issues like nutrient pollution.
5. Understanding the nitrogen cycle is crucial for managing agricultural practices and mitigating climate change impacts, as it influences soil fertility and greenhouse gas emissions.

Review Questions

• How do the processes of nitrogen fixation and nitrification contribute to the availability of nitrogen for plant growth?
  • Nitrogen fixation converts atmospheric nitrogen into ammonia, making it available for plants. This ammonia can then be further processed through nitrification, where it is converted into nitrites and then nitrates. Nitrates are a form of nitrogen that plants can readily absorb and utilize for growth, thereby linking these two processes directly to plant health and productivity.
• In what ways does human activity impact the natural nitrogen cycle, particularly through agriculture and urbanization?
  • Human activities significantly impact the natural nitrogen cycle through the use of synthetic fertilizers in agriculture, which increases the amount of reactive nitrogen in ecosystems. This excess can lead to nutrient pollution in waterways, causing algal blooms and other ecological disruptions. Urbanization also contributes through increased emissions from vehicles and industries, further altering nitrogen levels in both soil and air.
• Evaluate the role of denitrification in the context of global climate change and how it interacts with other biogeochemical cycles.
  • Denitrification plays a vital role in removing excess nitrates from ecosystems, helping to mitigate nutrient pollution. This process returns nitrogen to the atmosphere as N₂ or N₂O, the latter being a potent greenhouse gas. Understanding denitrification's relationship with carbon cycling is crucial for addressing climate change, as both cycles interact through microbial processes that affect soil health and greenhouse gas emissions.

Related terms

Nitrogen fixation: The process by which atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or related compounds in soil and water, primarily by certain bacteria and lightning.

Nitrification:

A microbial process that converts ammonia into nitrites (NO₂⁻) and then into nitrates (NO₃⁻), making nitrogen available for plant uptake.

Denitrification:

The process through which nitrates are reduced to nitrogen gas (N₂) or nitrous oxide (N₂O) by microorganisms, returning nitrogen to the atmosphere.