The roots of the plant act as miners moving through the soil and bringing needed minerals into the plant roots. However, the nitrogen in the atmosphere is not in a form that plants can utilize. These plants tend to have root nodules in which the nitrogen-fixing bacteria live. Not all bacteria utilize the above route of nitrogen fixation. Many that live free in the soil, utilize other chemical pathways.
Roots have extensions of the root epidemal cells known as root hairs.
Denitrifying turn nitrate back into nitrogen. Covalently bonded N2 molecules are very stable. Only prokaryotes like Rhizobium can fix nitrogen. This bacterium lives in root nodules and fixes nitrogen in the absence of oxygen. It is also present in soil.