Question

How can nitrogen be fixed naturally for plant use?

Answer 1

Nitrogen is also an essential nutrient which is needed for plant growth & the development but is usually unavailable in its most prevalent form as the atmospheric nitrogen. Plants instead also depend upon the combined, or fixed, forms of nitrogen, like the ammonia and the nitrate.

Complete answer:
Nitrogen fixation is known as a process by which the nitrogen in the atmosphere gets converted in the form of ammonia.

Many heterotrophic bacteria usually reside in the soil & fix the high levels of the nitrogen without the direct interaction with other organisms. Eg of such type of the nitrogen-fixing bacterias generally includes the species of the Azotobacter, or the Bacillus, the Clostridium, and the Klebsiella. Such organisms then also have to find their own source of energy, which is typically by an oxidizing organic molecule which gets released by the other organisms or from the process called as decomposition.

Many microorganisms fix the nitrogen symbiotically by partnering with a host plant. The plant usually produces sugars from the photosynthesis which is then utilized by the nitrogen-fixing microorganism for the energy which it needs for the nitrogen fixation. In exchange for these carbon sources, the microbes then provide the fixed nitrogen to the other host plant for its growth. One good example of this type of nitrogen fixation is known as the water fern Azolla’s symbiosis with a cyanobacterium Anabaena azollae.
The Rhizobium or the Bradyrhizobium bacteria then colonize most of the host plant’s root system & then cause the roots to form the nodules that house the bacteria. The bacteria then begins to fix the nitrogen which is needed by the plant. Access to this fixed nitrogen then allows the plant to produce leaves which gets fortified with nitrogen that can be recycled throughout the plant. This then allows the plant to increase the photosynthetic capacity, which in turn yields nitrogen-rich seed.
Much of this nitrogen is usually provided to the cropping systems in the form of industrially produced nitrogen fertilizers. Use of such fertilizers has led to a large scale worldwide ecological problems, like the formation of the coastal dead zones.

Note: Biological nitrogen fixation, on the other hand, usually offers a natural means of providing nitrogen for the plants. It is also a critical component of many aquatic, as well as the terrestrial ecosystems across our biosphere.