Decomposers play a key role in an ecosystem by breaking down dead organic matter, returning nutrients to the soil, and facilitating nutrient cycling. Organisms such as bacteria and fungi decompose materials, recycling essential elements like carbon, nitrogen, and phosphorus, which are crucial for plant growth. This process helps maintain the health of the ecosystem by preventing nutrient depletion. Without decomposers, ecosystems would accumulate waste and suffer from a reduction in nutrient availability.