ABSTRACT
The origin of practically all of the organic matter in soils and terrestrial ecosystems is from green plants, although the organic matter of green plants is generally cycled through other kinds of organisms before becoming a component of soil organic matter (Chapters 8 and 9). Leaves falling to the ground accumulate in a litter layer of plant detritus that includes dead stems and branches. The organic tissues in this layer are shredded by invertebrate animals and gradually decomposed by microorganisms. Organic residues from the decomposition of plant stems, branches, and leaves accumulate at the ground surface, unless animals carry them into the soil. Earthworms, ants, and termites are notable among the animals that carry organic matter down in soils. Burrowing mammals are responsible for some mixing in soils, but generally much less than by arthropods (for example, insects, mites, centipedes, millipedes, and segmented (oligochaete) worms). Plant root decay is responsible for much of the organic matter that accumulates within soils.
