Why is a root nodule a nutritional adaptation of a plant?

Adaptation is a positive value for plants. Adaptation leads to evolution and better survival in an organism. Various plants modified their parts to survive in stressful environments. These are called adaptations.

Plants cannot fix nitrogen from the atmosphere directly. Some soil microbes help in nitrogen fixation. This is called biological nitrogen fixation because other living organisms are involved in this process. Nodules in the roots have resulted from the association of bacteria with the plant root system.

Atmospheric nitrogen can not be fixed directly by the plants. Therefore these bacteria fix the gaseous nitrogen from the atmosphere and convert it into nitrite and nitrate that can be easily used by plants. Nodules act as an adaptive modification in roots that provide nutrition to the plants from the soil. Therefore, Root nodules are a nutritional adaptation of a plant.