Nitrogen-fixing bacteria

Definition

Nitrogen-fixing bacteria are microorganisms that convert atmospheric nitrogen ($$N_2$$) into ammonia ($$NH_3$$), a form that plants can readily use for growth. These bacteria play a vital role in the nitrogen cycle, facilitating the process of nitrogen fixation, which is essential for replenishing soil nitrogen levels and supporting plant nutrition.

5 Must Know Facts For Your Next Test

1. Nitrogen-fixing bacteria include free-living species like Azotobacter and symbiotic species such as Rhizobium, which forms nodules on legume roots.
2. These bacteria are crucial for maintaining soil fertility because they naturally provide ammonia, which is a key nutrient for plant growth.
3. The process of nitrogen fixation is energy-intensive and requires specific enzymes, like nitrogenase, to break the strong triple bond of atmospheric nitrogen.
4. In addition to legumes, some non-leguminous plants, like alder trees, also form symbiotic relationships with nitrogen-fixing bacteria.
5. Agricultural practices often utilize crop rotation with legumes to enhance soil nitrogen levels through the activity of nitrogen-fixing bacteria.

Review Questions

• How do nitrogen-fixing bacteria contribute to soil fertility and plant growth?
  • Nitrogen-fixing bacteria are essential for soil fertility as they convert atmospheric nitrogen into ammonia, a form that plants can absorb and utilize. This process enriches the soil with a vital nutrient, supporting plant growth and development. By forming symbiotic relationships with plants, especially legumes, these bacteria help maintain sustainable agricultural practices by naturally replenishing soil nitrogen levels.
• Discuss the relationship between nitrogen-fixing bacteria and other processes in the nitrogen cycle, such as nitrification and denitrification.
  • Nitrogen-fixing bacteria initiate the nitrogen cycle by converting atmospheric nitrogen into ammonia. This ammonia can then be further processed by nitrifying bacteria into nitrites and nitrates, which are forms usable by most plants. Additionally, denitrifying bacteria play a crucial role by converting excess nitrates back into atmospheric nitrogen, thus completing the cycle. Together, these processes ensure a continuous supply of available nitrogen for ecosystems.
• Evaluate the impact of agricultural practices on the efficiency of nitrogen-fixing bacteria and overall soil health.
  • Agricultural practices significantly impact the efficiency of nitrogen-fixing bacteria and soil health. Practices like monoculture can deplete soil nutrients and reduce the populations of beneficial microbes, including nitrogen fixers. In contrast, incorporating crop rotations with legumes can enhance the activity of these bacteria and improve soil fertility. Sustainable practices that promote biodiversity and reduce chemical fertilizers not only support healthy populations of nitrogen-fixing bacteria but also contribute to long-term soil health and ecosystem stability.

Related terms

ammonification: The process by which organic nitrogen from dead plants and animals is converted into ammonia by decomposing microorganisms.

nitrification: The biological process in which ammonia is oxidized to nitrite ($$NO_2^-$$) and then to nitrate ($$NO_3^-$$) by nitrifying bacteria, making nitrogen accessible to plants.

denitrification: The microbial process that converts nitrates ($$NO_3^-$$) back into nitrogen gas ($$N_2$$), returning it to the atmosphere and completing the nitrogen cycle.