Question

What is the biological significance of Azolla pinnata in agriculture?

Answer 1

The aquatic fern- Azolla pinnata has a symbiotic association with nitrogen fixing cyanobacteria, Anabaena azollae. It grows in the rice fields and brings about soil enrichment by fixing atmospheric $N_2$ into nitrates that can be absorbed by the plants. This decreases the requirement of adding synthetic Nitrogen containing fertilizers to the soil. As a result the soil is enriched with nutrients without damaging its microflora/fauna