Nitrogen Fixation Overview
Nitrogen fixation is the process through which atmospheric nitrogen (N₂) is converted into ammonia (NH₃), a form usable by plants. Biological nitrogen fixation is primarily carried out by certain bacteria and archaea, which possess the enzyme nitrogenase.

Key Biological Nitrogen Fixers
- **Symbiotic Nitrogen Fixers**:
- These organisms form a mutualistic relationship with plants, most notably legumes.
- Examples include *Rhizobium* species, which colonize root nodules of legumes, converting atmospheric nitrogen into ammonia.
- **Free-Living Nitrogen Fixers**:
- These bacteria do not require a plant host and can be found in the soil or water.
- Notable genera include *Azotobacter* and *Clostridium*, which fix nitrogen independently.

Process of Biological Nitrogen Fixation
- **Nitrogenase Enzyme**:
- The key enzyme that facilitates the conversion of nitrogen gas to ammonia.
- This process occurs under anaerobic conditions, as oxygen can inhibit nitrogenase activity.
- **Energy Requirement**:
- The fixation of nitrogen is an energy-intensive process, requiring ATP.
- Bacteria often rely on carbohydrates derived from their host plants or organic matter in the environment.

Importance of Nitrogen Fixation
- **Soil Fertility**:
- Biological nitrogen fixation enriches soil nutrient content, promoting plant growth.
- **Sustainable Agriculture**:
- Utilizing nitrogen-fixing crops reduces the need for synthetic fertilizers, leading to more sustainable farming practices.
- **Ecosystem Health**:
- Enhances biodiversity and supports various trophic levels by providing essential nutrients to primary producers.
In summary, biological nitrogen fixation is vital for enhancing soil fertility, supporting sustainable agriculture, and maintaining ecosystem health.