root nodules

Root nodules are small, swollen lumps on the roots of legume plants (like peas, beans, and lentils) where helpful bacteria live.

• They form when a bacterium called Rhizobium enters young roots and the plant grows a special “home” around it.
• Inside nodules, Rhizobium does nitrogen fixation: it changes nitrogen gas from the air (which plants cannot use directly) into nitrogen compounds that plants can use to make proteins and grow well.
• It is a mutual partnership: the plant gives the bacteria food (sugars) and shelter, and the bacteria provide usable nitrogen to the plant.
• Many active nodules look pinkish inside because of a pigment (leghemoglobin) that helps control oxygen—Rhizobium needs oxygen, but too much oxygen can disturb nitrogen fixation.
• This is one reason legume crops can improve soil fertility, helping the next crop grow better with less need for chemical fertilisers.

Think of root nodules as tiny “natural fertiliser factories” attached to the roots.