Nitrogen Fixing Plants

It has been observed that questions related to Nitrogen fixing plants often come in UPSC and various other exams. In this article, we give a brief on Nitrogen Fixing Plants, their types, etc. which are useful UPSC notes.

Plants obtain their inorganic nutrients from air, water, and soil. Plants absorb a wide variety of mineral elements. Not all the mineral elements that they absorb are required by plants. Out of the more than 105 elements discovered, about 21 are essential and beneficial for normal plant growth and development.

Macro-nutrients: The elements that are required in large quantities are called macronutrients.

Micro-nutrients: The elements that are required in less quantities or in trace are termed as micronutrients. These elements are either essential constituents of proteins, carbohydrates, fats, nucleic acid etc., and take part in various metabolic processes. Deficiency of each of these essential elements may lead to symptoms called deficiency symptoms.

Importance of Nitrogen in Plants

Nitrogen is very essential for the sustenance of life. Apart from carbon, hydrogen and oxygen, nitrogen is the most prevalent element in living organisms. Nitrogen is a constituent of amino acids, proteins, hormones, chlorophylls and many of the vitamins. Plants compete with microbes for the limited nitrogen that is available in soil. Thus, nitrogen is a limiting nutrient for both natural and agricultural eco-systems.

Atmospheric Nitrogen: Nitrogen constitutes about 78% of air. However, plants cannot use atmospheric nitrogen directly.

Nitrogen exists as two nitrogen atoms joined by a very strong triple covalent bond (N ≡ N).

What is Nitrogen Fixation?

The process of conversion of nitrogen (N2) to ammonia is termed as nitrogen fixation.

Alternatively it can be said that nitrogen fixation is a process that implies the transformation of the relatively non-reactive atmospheric N2 into its more reactive compounds (nitrates, nitrites, or ammonia).

Chemically, N fixation is splitting the triple bond in N2 and reducing it to ammonia (NH3) or ammonium (NH4+). The process is sometimes referred to as dinitrogen fixation, considering the two atoms in the N2 formula.

In nature, lightning and ultraviolet radiation provide enough energy to convert nitrogen to nitrogen oxides (NO, NO2, N2O). Industrial combustions, forest fires, automobile exhausts and power-generating stations are also sources of atmospheric nitrogen oxides.

Ammonification: Decomposition of organic nitrogen of dead plants and animals into ammonia is called ammonification.

Biological Nitrogen Fixation

Very few living organisms can utilise the nitrogen in the form N2, available abundantly in the air. Only certain prokaryotic species are capable of fixing nitrogen. Reduction of nitrogen to ammonia by living organisms is called biological nitrogen fixation. The enzyme, nitrogenase which is capable of nitrogen reduction is present exclusively in prokaryotes. Such microbes are called N2- fixers.

What are Nitrogen Fixing Plants?

A nitrogen fixing plant is a natural way to provide plant-adjusted nitrogen without any industrial harm to nature. Using them in crop rotation allows nitrogen fixation for succeeding plants. Another successful practice is to use nitrogen-fixing plant species in intercropping.

Types of Nitrogen Fixing Plants

Primarily there are three types of Nitrogen Fixing Plants. These are

1. Clovers
2. Vetches, and
3. Peas

Clovers: Clovers are generally short-lived herbs and feature alternate compound leaves, usually with three-toothed leaflets Nitrogen Fixing Plants. They belong to the legume family. Most of these are cultivated as fodder crops.

Vetches: Vetches are pea-like leguminous Nitrogen Fixing Plants.

Peas: Peas are Nitrogen Fixing Plants or legumes that can fix nitrogen through a symbiotic relationship with Rhizobia bacteria in their roots. The bacteria take nitrogen from the air and convert it to ammonia, which the plant can then use. In exchange, the plant provides carbohydrates to the bacteria.

It includes beans, fava (aka faba, broad), alfalfa, green (aka French), runner, field, sweet, peanuts (aka groundnuts), soybeans, cream, black-eyed, or purple-hulled beans, lupins, lentils, cowpeas, chickpeas.

Also read: Nitrogen fixing plants UPSC PYQ

Nitrogen Fixation: N-Fixing Plants And Bacteria