Rhizobium bacteria are important for plants because plants cannot use nitrogen from the air.
Explanation:
Rhizobium bacteria are micro organisms that fix nitrogen available in the atmosphere.
For nitrogen fixing, they need to associate with plants. They cannot do it independently.
So they make use of a plant host like legumes. In the roots of such plants, they fix nitrogen in the air to ammonia and other organic compounds. This is very useful for improving the soil fertility.
In return, the plants give compounds prepared by photosynthesis for its survival. So the relationship is mutually beneficial.
