Nitrogen fixing organism which can be free as well as symbiotic is

A free living nitrogen fixing cyanobacterium which can also form symbiotic association with the water fern Azolla is:

A free living nitrogen fixing cyanobacterium which can also form symbiotic association with the water fern Azolla ………….. .

Azolla enriches rice fields with nitrogen due to its association with Or A free living nitrogen fixing cyanobacterium which can also form symbiotic association with the water fern Azolla is