Decomposition

Decomposition is the process by which decomposers break detritus — dead plants, dead animals and their excreta — down into simple organic and inorganic matter, and it is essential for recycling nutrients and keeping an ecosystem's nutrient pool in balance. How fast decomposition proceeds depends on the chemical nature of the material involved: compounds such as carbohydrate, fat and protein decompose quickly, while cellulose, lignin, chitin, hair and bone resist breakdown and decompose far more slowly. Mechanistically, decomposition is a stepwise, enzyme-driven process with five recognised stages. Fragmentation is the physical breaking-down of detritus into smaller particles by detritivores such as bacteria, fungi and earthworms, which also secrete substances that increase the particles' surface area and speed the process along. Catabolism is the stage where decomposers secrete extracellular enzymes into their surroundings to chemically break complex organic and inorganic compounds down into simpler ones. Leaching (eluviation) is the physical movement of the now water-soluble organic and inorganic compounds from the soil surface down to lower layers, carried by water. Humification converts the simplified detritus into a dark, amorphous substance called humus, which is highly resistant to further microbial attack (so decomposition slows sharply here) and which acts as a long-term reservoir of nutrients. Mineralisation is the final stage, in which specific microbes release inorganic nutrien …