Nitrogen fixation in root nodules of Alnus is brought about by

Options

A. Frankia
B. Azorhizobium
C. Bradyrhizobium
D. Clostridium

Answer

To answer the question "Nitrogen fixation in root nodules of Alnus is brought about by," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen fixation is the process of converting atmospheric nitrogen (N₂) into a form that plants can use, such as ammonia (NH₃). This process is essential for plant growth since nitrogen is a vital nutrient.

2. **Identifying the Organisms Involved**:
- Various bacteria are known to fix nitrogen. Some of these include:
- **Rhizobium**: Typically associated with leguminous plants.
- **Frankia**: Associated with non-leguminous plants like Alnus (alders).
- **Clostridium**: Free-living nitrogen-fixing bacteria.
- **Bradyhizobium**: Symbiotic with certain legumes.

3. **Focus on Alnus**:
- Alnus, commonly known as alder, is a non-leguminous plant. It forms symbiotic relationships with specific nitrogen-fixing bacteria.

4. **Correct Identification**:
- Among the options provided, **Frankia** is the actinomycete that forms root nodules in Alnus and is responsible for nitrogen fixation in this plant.

5. **Conclusion**:
- Therefore, the correct answer to the question is **Frankia**.

### Final Answer:
Nitrogen fixation in root nodules of Alnus is brought about by **Frankia**.

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