Which of the following statements is correct?

Options

A. Azotobacter fixes atmospheric nitrogen in the nodules of legumes.
B. Certain cyanobacteria like Anabaena can fix nitrogen in paddy fields
C. Azospirillium species fixes nitrogen in chick-pea
D. Mycorrhiza absorb nitrates from soil and provide it to the plant.

Answer

To determine which of the statements is correct, let's analyze each statement step by step:

1. **Statement 1: Azotobacter fixes atmospheric nitrogen in the nodules of legumes.**
- Azotobacter is a free-living nitrogen-fixing bacterium. It does not form nodules on legumes; instead, Rhizobium is the bacterium that forms nodules in legumes. Therefore, this statement is incorrect.

2. **Statement 2: Anabena can fix nitrogen in the paddy fields.**
- Anabena is a cyanobacterium that can fix nitrogen, but it does not do so specifically in association with paddy fields. The bacteria that are typically associated with paddy fields for nitrogen fixation are Azoospirillum. Hence, this statement is also incorrect.

3. **Statement 3: Azoospirillum species fixes nitrogen in chickpea.**
- Azoospirillum is known for its role in nitrogen fixation in paddy fields, not specifically in chickpeas. This statement is incorrect as well.

4. **Statement 4: Mycorrhiza absorb nitrates from the soil and provide it to the plants.**
- Mycorrhizae are a symbiotic association between fungi and plant roots. They help in the absorption of water and nutrients (including nitrates) from the soil and provide them to the plants. This statement is correct.

Based on the analysis, the correct statement is:
**Statement 4: Mycorrhiza absorb nitrates from the soil and provide it to the plants.**