Variation in hopanoid composition and abundance in forest soils during litter decomposition and humification

The structures and concentrations of hopanoids, a family of pentacyclic triterpenoids, were analysed to determine their contribution to the alkyl carbon with increasing soil depth of a Haplic Podzol (from the Oi to the Bs horizon). After the isolation of solvent-extractable hopanoids, the soil samples were subjected to sequential chemical degradation comprising the cleavage of ester and ether bonds and the oxidative cleavage of aliphatic–aromatic carbon linkages between hopanoids and the macromolecular organic matrix. Identification and quantification of the substances investigated were carried out by GC–MS. On the basis of the different analytical steps hopanoids were released as hydrocarbons, alcohols, and acids, with 31 up to 35 carbon atoms. No hopanoids were found in the Oi horizon; the concentrations rose markedly from the Oe to the Oa and E1 horizon (up to 565 μg g−1 total organic carbon) showing a minimum in the E2 horizon and a second maximum in the Bs horizon. The behaviour of these substances with increasing depth can be explained by varying activity of hopanoid-producing microorganisms and/or translocation processes due to podzolization. Because of the low concentrations, hopanoids and other triterpenoids do not play an important role in the enrichment of alkyl-carbon compounds during litter decomposition and humification in the forest soil under study.