Question

Non-symbiotic nitrogen fixers are

• A. Azotobacter
• B. Pseudomonas
• C. soil fungi
• D. blue-green algae

Answer 1

The Correct Option is A

The question pertains to the identification of non-symbiotic nitrogen fixers. Let's discuss each option to understand why Azotobacter is the correct answer.

1. Azotobacter: These are free-living nitrogen-fixing bacteria found in soil. They convert atmospheric nitrogen into ammonia, which plants can uptake as a nutrient. As they do not rely on a host, they are considered non-symbiotic nitrogen fixers.
2. Pseudomonas: While certain species of Pseudomonas are known for their plant growth-promoting capabilities, they are not primarily known for nitrogen fixation. They are more associated with the degradation of organic matter and biocontrol of other microbes.
3. Soil fungi: Generally, fungi play significant roles in decomposing organic matter and forming symbiotic associations with plants, such as mycorrhiza. However, they are not known for fixing atmospheric nitrogen non-symbiotically.
4. Blue-Green Algae (Cyanobacteria): Although cyanobacteria fix nitrogen, many of them form symbiotic relationships with water plants or lichens. However, some, like those in rice paddies, can act non-symbiotically, but the question context does not primarily associate them as free-living in soil like Azotobacter.

Conclusion: Based on above logic, Azotobacter is most commonly recognized as a non-symbiotic nitrogen fixer.