Question

Which aquatic fern performs nitrogen fixation?
A. Azolla
B. Nostoc
C. Salvia
D. Salvinia

Answer 1

Hint: Let us recall that nitrogen fixation is basically the process of conversion of molecular nitrogen in air to ammonia and it is naturally carried out by several microorganisms having symbiotic relationship with the plant groups especially legumes.

Complete answer:
As we have learnt that nitrogen fixation is the process of conversion of molecular nitrogen in air to ammonia and it is naturally carried out by several microorganisms having symbiotic relationship with the plant groups especially legumes.
Let us talk about the given microorganisms, among them Azolla is a free floating aquatic fern which is inoculated in the rice field to increase the yield. It contains the blue green algae Nostoc and Anabaena in its leaf cavities which are responsible for the formation of symbiotic relationship with the host plant and help in fixation of nitrogen.
It is responsible for the release of approximately fixed nitrogen.
Salvia is a genus of mint family and is used as herb or ornamental plants and aromatic foliage. Salvia hispanica species of this family produces edible seeds that are high in proteins and fats.
Salvinia is also a free floating fern and it is commonly known as Watermoss but it does not help in fixing nitrogen rather it grows very fast and forms a dense mat over the still water choking off the microorganisms and other animals present in that water. These plants become saturated with oil in a very less period of time and hence are considered as mops of oils.
 Therefore from the above explanation we can say that Azolla is the one which is responsible for nitrogen fixation.

Hence the correct answer is (A).

Note: Some interesting facts about Azolla:
Azolla is the most widely used green manure for rice crops in Asia as it has a high growth rate, nitrogen fixing ability and the capacity to scavenge nutrients from soil and water.
This fer doubles its biomass within 2-5 days under ideal environmental conditions.
It helps in preventing the increase of pH, reduces water temperature, suppresses weeds and mosquito proliferation.