Decomposition is the final stage in the cycling of matter and energy flow in an ecosystem. Although, they are not shown in most food chains, decomposers form a link between producers, consumers, and the biotic environment. Organisms involved in the decomposition process are known as decomposers. They play a vital role in the decaying process as a way of nutrient cycling in an ecosystem. Decomposers are saprophytes (organisms that feed on dead and decaying organisms). Saprophytes include all fungi and certain bacteria and earthworms. Some saprophytes such as mushrooms, mould, maggots of some dipterans, e.g., house flies, snails, and earthworms that can easily be seen, are known as macro-decomposers.
Bacteria and many others that cannot be seen with the naked eye, except with the aid of microscopes are known as micro-decomposers.
When plants and animals die, their bodies decay by the activities of decomposers which feed on them. The decomposers first secrete enzymes onto their food source, (dead materials) which breakdown complex organic compounds like carbohydrates and proteins into simple soluble inorganic compounds. Decomposers only absorb a small amount of nutrients and energy for their use. The rest is released into the soil, air and water. As decay gets underway, the rotten materials may get warm due to heat given out by the decomposers. Inorganic compounds released during decay include gases like carbon dioxide (CO2), ammonia (NH3), hydrogen sulphide (H2S) and water vapour.
These gases (especially H2S) are what give it an unpleasant smell. Water or moisture usually accelerates the rate of decay. The only abiotic (non-living) decomposer is fire in the forest and Savannahs. Its activities help to release some important compounds such as nitrates, potassium, sulphates and phosphates which return to the abiotic environment. These are used by green plants to produce chemical energy from sunlight.