A) Azolla
B) Nostoc
C) Anabaena
D) Clostridium
Correct Answer: A
Solution :
Azolla, a small aquatic fem has a small cavity on the uppermost part of the leaf which houses different blue-green algae belonging to Anabaena azollae. These blue-green algae have the ability to fix atmospheric nitrogen, available to Azolla. The use of Azolla in rice yields at the rate of 200 gm per square metre area can increase rice yield by 12-38%. Experiments have revealed that application of 10 tonnes of fresh Azolla biomass in one hectare, adds as much as 100 kg nitrogen. Cyanobacteria like Anabaena, Nostoc etc fix atmospheric nitrogen and also derive energy for his by carrying out photosynthesis. They also secrete growth hormones (vitamin\[\text{-}{{\text{B}}_{\text{12}}}\] auxins, ascorbic acid). The use of cyanobacteria is confined only to rice crop.
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