The primary role of legumes in an ecosystem is to fix nitrogen from the atmosphere into a form that plants can utilize, enhancing soil fertility. This process is facilitated by symbiotic bacteria residing in the root nodules of leguminous plants. By converting atmospheric nitrogen into ammonia, legumes enrich the soil, benefiting other plants that cannot fix nitrogen on their own. This natural fertilization process plays a significant role in sustainable agriculture and is essential for healthy soil ecosystems.