This chapter studies the organic matter dynamics in the forest soils of temperate and tropical ecosystems by detailed morphological observations, including micromorphology, and a combination of spectroscopic and chemical degradation methods. It discusses the primary resources like plant debris that are related to the parent materials of humification. Research is conducted to elucidate the role of secondary resources like microbial and animal residues, and of black carbon as a possible source of humic materials. The pathways of humification differ according to the chemical composition of the resources. Microbial resynthesis is important for proteins and carbohydrates, but protection of polysaccharides by recalcitrant molecules may occur. Mineralization of carbohydrates is responsible for the decline of O-alkyl C from the soil surface down to the deepest forest soil A subhorizon. Within the forest soil profiles, lignin is altered by side-chain oxidation, demethoxylation, and loss of phenolic structures. The evident increase of aryl C in humus-rich mineral soils is the result of a relative accumulation of the stable nonlignin structures. The chapter also discusses the dynamics of alkyl-C compounds.
