Decomposers are organisms that break down dead or decaying organisms, and in doing so,they carry out the natural process of decomposition. Like herbivores and predators, decomposers are heterotrophic, meaning that they use organic substrates to get their energy, carbon and nutrients for growth and development. While the terms decomposer and detritivore are often interchangeably used, however, detritivores must digest dead matter via internal processes while decomposers can break down cells of other organisms using biochemical reactions without need for internal digestion. Thus, invertebrates such as earthworms, woodlice, and sea cucumbers are detritivores, not decomposers, in the technical sense, since they must ingest nutrients and are unable to absorb them externally.
The primary decomposers of litter in many ecosystems are fungi. Unlike bacteria, which are unicellular organisms, most saprotrophic fungi grow as a branching network of hyphae. While bacteria are restricted to growing and feeding on the exposed surfaces of organic matter, fungi can use their hyphae to penetrate larger pieces of organic matter. Additionally, only wood-decay fungi have evolved the enzymes necessary to decompose lignin, a chemically complex substance found in wood. These two factors make fungi the primary decomposers in forests, where litter has high concentrations of lignin and often occurs in large pieces. Fungi decompose organic matter by releasing enzymes to break down the decaying material, after which they absorb the nutrients in the decaying material. Hyphae used to break down matter and absorb nutrients are also used in reproduction. When two compatible fungi's hyphae grow close to each other, they will then fuse together for reproduction and form another fungus.
- NOAA. ACE Basin National Estuarine Research Reserve: Decomposers.
- C.Michael Hogan. 2011.Trophic level. Eds. M.McGinley & C.J.cleveland. Encyclopedia of Earth. National Council for Science and the Environment. Washington DC
- Blanchette, Robert (September 1991). "Delignification by Wood-Decay Fungi". Annual Review of Phytopathology 29: 281–403. doi:10.1146/annurev.py.29.090191.002121. Retrieved 20 April 2015.
- Waggoner, Ben; Speer, Brian. "Fungi: Life History and Ecology". Introduction to the Fungi. Retrieved 24 January 2014.
- Beare, MH; Hendrix, PF; Cheng, W (1992). "Microbial and faunal interactions and effects on litter nitrogen and decomposition in agroecosystems". Ecological Monographs 62: 569–591. doi:10.2307/2937317.
- Hunt HW, Colema9n DC, Ingham ER, Ingham RE, Elliot ET, Moore JC, Rose SL, Reid CPP, Morley CR (1987) "The detrital food web in a shortgrass prairie". Biology and Fertility of Soils 3: 57-68
- Smith TM, Smith RL (2006) Elements of Ecology. Sixth edition. Benjamin Cummings, San Francisco, CA.