Question

nitrogen fixation of rice fields can be low in the presence of which one of the following type organisms :-- water fern , green algae, brown algae, mosses​

Answer 1

Explanation:

Azolla is a floating pteridophyte, which contains as endosymbiont the nitrogen-fixing cyanobacterium Anabaena azollae (Nostocaceae family). Widely cultivated in the Asian regions, Azolla is either incorporated into the soil before rice transplanting or grown as a dual crop along with rice. To examine the feasibility of its use in flooded rice fields sited in the Temperate European Areas, we carried out a series of experiments in PVC tanks during 2000–2002 in Po Valley (northern Italy) conditions, to study the growth-development dynamics and the resistance/tolerance to low temperatures and to commonly used herbicides of several different Azolla strains. Three out of five strains tested survived the winter, with an increase in biomass from March to May producing approximately 30–40 kg  of nitrogen. One of these strains, named “Milan”, emerged as the most resistant to herbicide and the most productive. Of the herbicides tested, Propanil permitted the survival of growing Azolla.

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Answer 2

Nitrogen fixation of rice fields can be low in the presence of water fern.

• Water fern incorporates nitrogen into the soil before rice transplanting and can be said that it is grown as a dual crop along with rice.  
• A water fern named Azolla sp. is a symbiont.
• It incorporates well with the leaves of paddy rice.
• This way it provides a good source of nitrogen.
• Nitrogen fixation happens by the action of nitrogenase enzymes, which is a combination of dinitrogenase and dinitrogenase reductase.
• Hence water fern is the correct option.

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