Nitrogen-fixing bacteria

Definition

Nitrogen-fixing bacteria are microorganisms that convert atmospheric nitrogen ($$N_2$$) into ammonia ($$NH_3$$) or related compounds, making nitrogen accessible to plants. These bacteria play a critical role in the nitrogen cycle, facilitating nutrient availability in ecosystems and promoting plant growth by enriching the soil with usable forms of nitrogen.

5 Must Know Facts For Your Next Test

1. Nitrogen-fixing bacteria are found in various environments, including soil, water, and the root nodules of certain plants, especially legumes.
2. The two main types of nitrogen-fixing bacteria are free-living bacteria like Azotobacter and symbiotic bacteria such as Rhizobium, which associate with legume roots.
3. The process of nitrogen fixation requires energy, typically derived from the breakdown of carbohydrates produced during photosynthesis.
4. Nitrogen-fixing bacteria significantly contribute to soil fertility by increasing nitrogen content, essential for plant protein synthesis and overall growth.
5. In agriculture, the use of legumes as cover crops is a common practice to enhance soil nitrogen levels through the activity of associated nitrogen-fixing bacteria.

Review Questions

• How do nitrogen-fixing bacteria contribute to soil fertility and plant growth?
  • Nitrogen-fixing bacteria convert atmospheric nitrogen into forms that plants can use, such as ammonia. This process enriches the soil with available nitrogen, which is crucial for plant protein synthesis and overall growth. By enhancing soil fertility, these bacteria support healthy crop yields and contribute to the sustainability of agricultural practices.
• Compare and contrast the roles of free-living and symbiotic nitrogen-fixing bacteria in ecosystems.
  • Free-living nitrogen-fixing bacteria, such as Azotobacter, exist independently in the soil or water and fix nitrogen without a host plant. In contrast, symbiotic nitrogen-fixing bacteria like Rhizobium form mutualistic relationships with legumes, residing in root nodules and providing fixed nitrogen directly to the plant. Both types are essential for introducing bioavailable nitrogen into ecosystems but operate through different mechanisms and interactions with plants.
• Evaluate the impact of nitrogen-fixing bacteria on agricultural practices and environmental sustainability.
  • Nitrogen-fixing bacteria have a profound impact on agriculture by reducing the need for synthetic fertilizers, which can lead to environmental issues such as runoff and water pollution. By promoting the use of legumes and crop rotation practices that harness these bacteria's capabilities, farmers can enhance soil health and sustainability. This natural method of enriching soil with nitrogen supports biodiversity and decreases dependency on chemical inputs, contributing positively to ecological balance.

Related terms

Ammonification:

The process by which organic nitrogen is converted into ammonia by bacteria and fungi, providing a form of nitrogen that can be used by plants.

Nitrification:

The microbial process in which ammonia is oxidized to nitrites ($$NO_2^-$$) and then to nitrates ($$NO_3^-$$), making nitrogen further available for plant uptake.

Legumes: A family of plants that have symbiotic relationships with nitrogen-fixing bacteria, allowing them to thrive in nitrogen-poor soils.