There are a few plants such as beans and peas that love nitrogen gas. These plants are able to draw nitrogen gas from the air and store it in their roots. They are the ones commonly called nitrogen fixing plants. They are plants that are required when a person is seeking to have a successful garden. Without sufficient nitrogen, plants in a garden setting will fail. They will be unable to grow.

Also, it is important to know that nitrogen fixing plants don’t pull nitrogen from the air on their own. They actually need help from a common bacteria called Rhizobium. The bacteria infects legume plants such as peas and beans and uses the plant to help it draw nitrogen from the air. The bacteria converts this nitrogen gas and then stores it in the roots of the plant.

When plants store nitrogen gas in their roots, a lump it produced on the root called a nitrogen nodule. This is harmless to the plant, but very beneficial in a garden.

Fundamentally, nitrogen fixing plants and bacteria work together to store the nitrogen gas. As this is done, they are create a green warehouse for the garden. While they are growing, they release very little nitrogen into the soil. When they are done growing and die, their decomposition will release stored nitrogen and increase the total nitrogen content of the soil. Their deaths make nitrogen available and possible for plants to use later on.

More Info: en.wikipedia.org