Final answer:
Rhizobium is a nitrogen-fixing bacterium that forms a symbiotic relationship with legumes, creating nodules on roots where it converts atmospheric nitrogen into usable ammonia for the plant, benefiting both the plant and the surrounding soil.
Step-by-step explanation:
Rhizobium is the nitrogen-fixing partner of legumes, like clover, alfalfa, and beans. These soil bacteria, known collectively as rhizobia, form a symbiotic relationship with the roots of legumes. Within specialized structures called nodules on the plant's roots, rhizobia convert atmospheric nitrogen into ammonia through a process involving the enzyme nitrogenase.
Symbiotic nitrogen fixation not only benefits the plants by providing them with an essential nutrient, but it also contributes to soil fertility as some of the fixed nitrogen is left in the soil when the plants die. Moreover, this natural fertilization method is environmentally friendly and is particularly crucial in sustainable agriculture practices. Legumes benefit from this interaction by having access to an endlessly renewable nitrogen source: the atmosphere, while rhizobia benefit from receiving carbohydrates produced by the plant through photosynthesis.