Nitrogen fixation

Definition

Nitrogen fixation is the process of converting atmospheric nitrogen gas (N₂) into a form that is usable by living organisms, typically ammonia (NH₃) or related compounds. This transformation is essential for sustaining life, as most organisms cannot utilize atmospheric nitrogen directly and rely on fixed nitrogen for the synthesis of amino acids and nucleotides.

5 Must Know Facts For Your Next Test

1. Nitrogen fixation occurs primarily through biological processes carried out by certain bacteria, including those found in the root nodules of leguminous plants.
2. Some cyanobacteria in marine environments also contribute significantly to nitrogen fixation, playing a crucial role in nutrient cycling in oceans.
3. This process is vital for estuarine ecosystems, as it helps maintain nitrogen levels that support diverse plant and animal life.
4. In salt marshes, nitrogen fixation contributes to the productivity of plant species such as Spartina, which can thrive in nutrient-poor conditions.
5. Human activities, such as the use of synthetic fertilizers, have increased nitrogen levels in aquatic systems, leading to issues like algal blooms and dead zones.

Review Questions

• How does nitrogen fixation support the productivity of estuarine ecosystems and salt marshes?
  • Nitrogen fixation plays a crucial role in supporting the productivity of estuarine ecosystems and salt marshes by providing bioavailable nitrogen that enhances plant growth. In these environments, nitrogen-fixing bacteria convert atmospheric nitrogen into forms that plants can absorb, which is especially important in nutrient-poor habitats. This process allows key species like Spartina to flourish, forming the foundation of the food web and supporting various aquatic organisms.
• Discuss the significance of nitrogen fixation within the context of nutrient cycling and energy flow in oceanic systems.
  • Nitrogen fixation is a critical component of nutrient cycling in oceanic systems because it transforms inert atmospheric nitrogen into biologically available forms. This conversion supports phytoplankton growth, which forms the base of marine food webs and contributes to energy flow within these ecosystems. The availability of fixed nitrogen influences primary productivity, impacting everything from fish populations to overall ecosystem health.
• Evaluate the ecological roles of marine bacteria and archaea in nitrogen fixation and its implications for marine biodiversity.
  • Marine bacteria and archaea are pivotal players in the nitrogen fixation process, significantly influencing marine biodiversity. By converting atmospheric nitrogen into accessible forms, they enhance nutrient availability for phytoplankton and macroalgae, which are essential for sustaining diverse marine life. The presence of these microorganisms supports not only primary producers but also higher trophic levels, highlighting the interconnectedness of marine ecosystems and the importance of maintaining healthy microbial communities.

Related terms

Ammonification: The process by which organic nitrogen is converted into ammonia, making it available for plants and other organisms.

Nitrification:

The conversion of ammonia into nitrites (NO₂⁻) and then nitrates (NO₃⁻) by bacteria, allowing plants to absorb these forms of nitrogen.

Leguminous plants: Plants that have symbiotic relationships with nitrogen-fixing bacteria, allowing them to convert atmospheric nitrogen into a form they can use for growth.