Answer:
The name of the bacteria that could be seen in the root of leguminous plants is Rhizobium. And the association is symbiotic association
They are like nitrogen replenishers of the soil, A plot of land being cultivated for a time might lose its fertility, And as a part of it there could be a decrease of nitrogen content in the soil. And this could affect the crops grown in the field as nitrogen is needed for plant growth. Thus by planting leguminous plants in this field which we have taken as an example, will bring in the rhizobium bacteria which will be present in the root nodules and these bacteria via symbiotic relationship will fix atmospheric nitrogen into the soil which brings back the fertility of the land.