In mature forest and grassland soils, the decomposition process establishs an equilibrium over time where litterfall additions equal the amount of organic matter decomposed. The rate of decomposition in a detritus food chain is controlled by many factors. In most terrestrial ecosystems, temperature and soil oxygen and moisture content tend to be the primary variables controlling the activities of decomposers. In some ecosystems, oxygen may not be readily available. In these cases aerobic respiration cannot take place, and the breakdown of organic compounds and energy extraction must then proceed by anaerobic means like fermentation .
Organisms involved in fermentation include bacteria and yeast.
Anaerobic decomposition releases much less energy from organic matter than does aerobic respiration. The end products of anaerobic decomposition include molecules such as carbon dioxide, water, and humus. They also include small-molecule alcohols, organic acids, ptomaines, amines, and other products, as well as gaseous substances such as methane. Because respiration is so much more efficient at releasing the energy contained in organic molecules, the activity of the detritus food chain is much higher in an aerobic environment, and the breakdown of materials more complete. Organic matter breakdown is substantially slower and less complete in anaerobic environments.