Which of the following can fix nitrogen in nonleguminous plants?

Options

A. Rhodospirillum
B. Azotobacter
C. Frankia
D. Rhizobium

Answer

To determine which bacteria can fix nitrogen in non-leguminous plants, we can analyze the options provided.

### Step-by-Step Solution:

1. **Understand Nitrogen Fixation**: Nitrogen fixation is the process by which certain bacteria convert atmospheric nitrogen (N₂) into ammonia (NH₃), which can be used by plants. While many bacteria that fix nitrogen are associated with leguminous plants, some can also associate with non-leguminous plants.

2. **Evaluate the Options**:
- **Option 1: Rhodospirillum**: This is a free-living nitrogen-fixing bacterium. It does not form symbiotic relationships with plants, particularly non-leguminous plants. Therefore, it cannot fix nitrogen in non-leguminous plants.
- **Option 2: Azotobacter**: Similar to Rhodospirillum, Azotobacter is also a free-living nitrogen-fixing bacterium. It does not associate with plants to fix nitrogen. Thus, this option is incorrect.
- **Option 3: Frankia**: Frankia is a genus of bacteria that forms symbiotic relationships with certain non-leguminous plants, such as alder trees. It is capable of fixing nitrogen in these plants, making this option correct.
- **Option 4: Rhizobium**: Rhizobium is well-known for its role in nitrogen fixation, but it specifically associates with leguminous plants (e.g., peas, beans). Therefore, this option is incorrect for non-leguminous plants.

3. **Conclusion**: Based on the evaluation, the correct answer is **Option 3: Frankia**, as it is the only bacterium listed that can fix nitrogen in non-leguminous plants.

### Final Answer:
**Frankia** is the bacterium that can fix nitrogen in non-leguminous plants.

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