Nitrogen fixation

Definition

Nitrogen fixation is the process by which nitrogen gas from the atmosphere is converted into ammonia or related compounds in soil, making it accessible for use by living organisms. This process is vital for ecosystems, as it directly contributes to the nitrogen cycle, enabling plants to grow and thrive by utilizing nitrogen compounds essential for their development.

5 Must Know Facts For Your Next Test

1. Nitrogen fixation can occur through biological processes, primarily facilitated by certain bacteria and archaea, as well as through abiotic processes such as lightning or industrial means.
2. The ammonia produced from nitrogen fixation can be further transformed into nitrates through nitrification, which plants can then absorb and use.
3. Leguminous plants, like beans and peas, have a symbiotic relationship with nitrogen-fixing bacteria, allowing them to thrive in nitrogen-poor soils.
4. Without nitrogen fixation, ecosystems would suffer from a deficiency of usable nitrogen, severely limiting plant growth and the entire food web.
5. Human activities, such as the use of fertilizers containing fixed nitrogen, have significantly altered natural nitrogen cycles, leading to environmental concerns like eutrophication.

Review Questions

• How does nitrogen fixation contribute to the overall health of an ecosystem?
  • Nitrogen fixation is essential for maintaining healthy ecosystems because it converts atmospheric nitrogen into forms that are accessible to plants. This process supports plant growth and productivity, which forms the basis of food webs. Without sufficient nitrogen available through fixation, plant growth would be stunted, negatively impacting herbivores and subsequently the entire ecosystem.
• Discuss the role of symbiotic bacteria in nitrogen fixation and their impact on plant life.
  • Symbiotic bacteria play a critical role in nitrogen fixation by converting atmospheric nitrogen into ammonia within root nodules of certain plants, particularly legumes. This relationship not only provides essential nutrients to the plants but also enhances soil fertility. By facilitating this process, these bacteria enable plants to thrive even in nitrogen-deficient soils, demonstrating a key interaction between organisms that boosts agricultural productivity.
• Evaluate the implications of human-induced changes to natural nitrogen cycles on ecosystems and agriculture.
  • Human activities, especially the widespread use of synthetic fertilizers containing fixed nitrogen, have significantly altered natural nitrogen cycles. While these practices enhance crop yields and food production in the short term, they can lead to negative environmental impacts such as soil degradation and water pollution through runoff. Eutrophication in aquatic ecosystems often results from excess nutrients, disrupting aquatic life and creating dead zones. These consequences highlight the need for sustainable practices that balance agricultural needs with ecological health.

Related terms

Nitrification: Nitrification is the biological oxidation of ammonia or ammonium to nitrite followed by the oxidation of nitrite to nitrate, which further helps plants access nitrogen.

Denitrification: Denitrification is the process where nitrates are reduced to nitrogen gas by microorganisms, returning nitrogen to the atmosphere and completing the nitrogen cycle.

Symbiotic bacteria: Symbiotic bacteria, such as Rhizobium, live in root nodules of legumes and play a key role in nitrogen fixation by converting atmospheric nitrogen into forms usable by plants.