Nitrogen cycle

Definition

The nitrogen cycle is a biogeochemical process that describes the transformation and movement of nitrogen through various environmental compartments, including the atmosphere, soil, and living organisms. It plays a crucial role in ecosystem structure and function by facilitating the availability of nitrogen, an essential nutrient for plants and animals, while also influencing the interactions within ecosystems and the broader Earth system.

5 Must Know Facts For Your Next Test

1. The nitrogen cycle involves several key processes: nitrogen fixation, nitrification, assimilation, ammonification, and denitrification.
2. Nitrogen is a vital nutrient for living organisms because it is a primary component of amino acids, proteins, and nucleic acids like DNA.
3. Human activities, such as fertilizer application and fossil fuel combustion, have significantly altered the nitrogen cycle, leading to environmental issues like eutrophication and air pollution.
4. Leguminous plants play an important role in the nitrogen cycle by hosting nitrogen-fixing bacteria in their root nodules, enhancing soil fertility.
5. The majority of Earth's atmospheric nitrogen is in the inert N2 form, which must be converted into reactive forms through natural processes to be utilized by living organisms.

Review Questions

• How do the processes of nitrification and denitrification interact within the nitrogen cycle?
  • Nitrification and denitrification are interconnected processes that help regulate nitrogen levels in ecosystems. Nitrification converts ammonia into nitrites and then nitrates, making nitrogen available for plant uptake. In contrast, denitrification reduces nitrates back to nitrogen gas, releasing it into the atmosphere. Together, these processes maintain a balance in nitrogen availability and help prevent excess accumulation of nitrates in soil and water.
• Evaluate how human activities impact the natural nitrogen cycle and what consequences arise from these changes.
  • Human activities, such as excessive fertilizer use in agriculture and fossil fuel combustion, have significantly disrupted the natural nitrogen cycle. This can lead to problems like eutrophication in aquatic systems, where nutrient overload causes harmful algal blooms and oxygen depletion. Additionally, increased nitrogen emissions can contribute to air pollution and respiratory issues. The alteration of this cycle poses risks to ecosystem health and biodiversity.
• Assess the role of nitrogen-fixing bacteria in enhancing ecosystem resilience within the context of the nitrogen cycle.
  • Nitrogen-fixing bacteria play a critical role in enhancing ecosystem resilience by converting atmospheric nitrogen into forms usable by plants. This process not only improves soil fertility but also supports diverse plant growth, leading to more stable ecosystems capable of withstanding environmental stressors. In ecosystems where these bacteria are present, plants can thrive even in nutrient-poor soils, promoting biodiversity and allowing for effective nutrient cycling within the larger context of the nitrogen cycle.

Related terms

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

Nitrification: A two-step microbial process that converts ammonia into nitrites (NO2-) and then into nitrates (NO3-), which are usable forms of nitrogen for plants.

Denitrification: The microbial process that converts nitrates back into atmospheric nitrogen (N2), completing the nitrogen cycle and releasing nitrogen gas into the atmosphere.