Microorganisms, particularly bacteria and fungi, are primary decomposers. They break down dead plants, animals, and waste products into simpler inorganic substances. This process, called decomposition, recycles essential nutrients (like carbon, nitrogen, and phosphorus) back into the soil and atmosphere, making them available for new plant growth. Without microbial decomposition, nutrients would be locked up in dead organic matter, preventing new life from thriving and disrupting entire ecosystems.