Decomposers such as bacteria, fungi and actinomycetes play an important role in the cycling of materials. They decompose the detritus (dead or partially decomposed animal or plant matter) so that the nutrients get stored in the soil to be utilised again by plants and animals. These absorbed nutrients are metabolically incorporated in plants during their growth. Decomposers act on the litter of vegetation, animal remains, faecal matter of animals (above ground detritus) and dead plant roots (below ground detritus), recycle the nutrients from them and return them to the soil. Dentrifying bacteria like Pseudomonas are decomposers involved in the conversion of nitrates to free nitrogen gas or ammonia to some other oxide. The free nitrogen returns to the atmospheric pool, whereas the oxides are assimilated by the plants.

Decomposers also play a major role in the carbon cycle, where carbon accumulated in wood is returned to the atmosphere through consumption and respiration by fungi, bacteria and other detritivores. Various anaerobic methanogenic bacteria present in freshwater wetlands, rice paddies and digestive tract of ruminants decompose organic matter to produce methane. Methane is a major component of natural gas and has the potential to increase global warming.