Variation in hopanoid composition and abundnce in forest soild during litter decomposition and humification

摘要

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 isoltion of solvent-extractable hopanoids, the soil samples were subjected to sequential chemical degradtion comprising the cleavage of ester and ther bonds and the oxidative cleavage of aliphatic-aromatic carbon linkages between hopanoids and the macromolecular organic matrix. Identification and quantification of the substances investigatd were carried out by GC-MS. On the basis of the different analytical steps hopanoids were released as hydro-carbons, alcohols, and acids, with 31 up to 35 carbon aotms. No hopanoids were found in the Oi horizon; the concentrations rose markedly from the Oe to the Oa and E1 horizon (up to 565 #mu#g 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 ht elow 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.