Which of the following are nitrogen-fixing plants?

UPSC Prelims 2022 Question:

Which of the following are nitrogen-fixing plants?

1. Alfalfa
2. Amaranth
3. Chickpea
4. Clover
5. Purslane (Kulfa)
6. Spinach

Select the correct answer using the code given below:

a) 1, 3 and 4 only

b) 1, 3, 5 and 6 only

c) 2, 4, 5 and 6 only

d) 1, 2, 4, 5 and 6

Correct Answer: Option a) 1, 3 and 4 only

Learn more about Nitrogen fixing plants in the given explanation below.

Explanation:

• Symbiotic nitrogen fixation by alfalfa provides substantial amounts of nitrogen (N) to livestock operations, subsequent crops, and soil organic matter. So, point 1 is correct.
• Chickpeas form root nodules that support biological N fixation (BNF) and host symbiotic N-fixing bacteria. So, point 3 is correct
• Nitrogen is "fixed" in clovers through a symbiotic relationship with Rhizobium bacteria that infects the plant's roots. The plant provides energy for the bacteria, and bacteria provide the "machinery" necessary to convert atmospheric nitrogen into a form available to plants. So, point 4 is correct.
• Amaranth, Purslane (Kulfa), Spinach are not nitrogen-fixing plants. So, points 2, 5 and 6 are not correct.

Types of Nitrogen Fixing Plants

There are two main types of nitrogen-fixing plants:

• Legumes: Legumes are a family of plants that includes beans, peas, lentils, peanuts, soybeans, and alfalfa. Legumes have a symbiotic relationship with bacteria called rhizobia, which live in the roots of the plants. The rhizobia bacteria convert atmospheric nitrogen into ammonia, which is then used by the legume plant.
• Non-legumes: There are also a number of non-leguminous nitrogen-fixing plants, such as actinorhizal plants (e.g., alders) and cyanobacteria (e.g., Nostoc). Actinorhizal plants have a symbiotic relationship with bacteria called Frankia, which live in the roots of the plants. Cyanobacteria are photosynthetic bacteria that can fix nitrogen from the atmosphere.

Here are some examples of nitrogen-fixing plants:

• Legumes: beans, peas, lentils, peanuts, soybeans, alfalfa, clover, vetch, lupins, chickpeas, cowpeas, mung beans, adzuki beans, lima beans, black-eyed peas
• Non-legumes: actinorhizal plants (e.g., alders, willows, poplars, sea buckthorn), cyanobacteria (e.g., Nostoc, Anabaena,Oscillatoria), azolla, mosquito fern, Gunnera, Blasia (liverwort), hornworts

 Therefore, option (a) is the correct answer.

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