Nitrogen Cycle

Definition

The nitrogen cycle is the biogeochemical process through which nitrogen is converted between its various chemical forms, including atmospheric nitrogen (N2), organic nitrogen, ammonia (NH3), and nitrates (NO3-). This cycle plays a crucial role in ecosystem health and function, supporting plant growth and influencing energy flow within food webs by providing essential nutrients to organisms.

5 Must Know Facts For Your Next Test

1. The nitrogen cycle involves multiple steps including nitrogen fixation, nitrification, assimilation, ammonification, and denitrification.
2. Nitrogen-fixing bacteria, such as Rhizobium found in root nodules of legumes, play a vital role in converting atmospheric nitrogen into a form usable by plants.
3. Human activities, such as the use of synthetic fertilizers and fossil fuel combustion, have significantly altered the nitrogen cycle, leading to issues like nutrient runoff and eutrophication in aquatic systems.
4. Eutrophication occurs when excess nitrates from agricultural runoff lead to algal blooms in water bodies, disrupting aquatic ecosystems by depleting oxygen levels.
5. The nitrogen cycle is interconnected with carbon and phosphorus cycles, all of which are essential for maintaining balanced ecosystems.

Review Questions

• How does the nitrogen cycle influence energy flow within an ecosystem?
  • The nitrogen cycle influences energy flow by providing essential nutrients that support plant growth. Plants absorb nitrates from the soil, which they use to create proteins and nucleic acids. As primary producers, these plants form the base of food webs, allowing energy to flow through herbivores and up to higher trophic levels. Without a healthy nitrogen cycle, plants would struggle to grow, disrupting the entire energy flow in the ecosystem.
• Evaluate the impact of human activities on the nitrogen cycle and its subsequent effects on aquatic biomes.
  • Human activities such as agricultural practices that use synthetic fertilizers have greatly disrupted the natural nitrogen cycle. These fertilizers contribute excess nitrates to runoff water, leading to nutrient pollution in aquatic biomes. This results in phenomena like eutrophication, where algal blooms occur due to high nutrient levels. The subsequent decay of these algae depletes oxygen in the water, harming aquatic life and disrupting the ecosystem balance.
• Synthesize information about how the interconnectedness of the nitrogen cycle with other biogeochemical cycles affects overall ecosystem stability.
  • The interconnectedness of the nitrogen cycle with carbon and phosphorus cycles is crucial for maintaining ecosystem stability. For example, while nitrogen is essential for protein synthesis in plants, carbon is vital for energy through photosynthesis. Disruptions in one cycle can lead to cascading effects on others; for instance, excess nitrogen can lead to increased plant biomass but reduced biodiversity if certain species outcompete others. Understanding these interactions helps illustrate the importance of balanced biogeochemical cycles for a stable ecosystem.

Related terms

Nitrogen Fixation: The process by which atmospheric nitrogen is converted into ammonia by certain bacteria, making it available for plant uptake.

Nitrification: The biological conversion of ammonia into nitrites (NO2-) and then nitrates (NO3-) by nitrifying bacteria, which can be taken up by plants.

Denitrification: The process by which nitrates are reduced to gaseous nitrogen (N2) by denitrifying bacteria, returning nitrogen to the atmosphere.