Characterisation of subfossil Sphagnum leaves, rootlets of ericaceae and their peat by pyrolysis-high-resolution gas chromatography-mass spectrometry

Abstract

A section from an oligotrophic peat and handpicked subfossil plant fragments from this peat were studied by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), an excellent method for the chemical characterisation of very small amounts of plant material. Leaves of peat mosses ( Sphagnum section Acutifolia) and rootlets of heathers (Ericaceae), both important contributors to this peat layer, were obtained by micromanipulation. The Py-GC-MS data consist of evaporation products of adsorbed compounds and a large number of pyrolysis products from remnants of the plant macromolecular systems. The Sphagnum pyrolysate consists mainly of compounds derived from polysaccharides, including anhydro sugars from xylose, mannose, galactose and glucose. Only a few phenolic compounds were observed in the peat moss sample. The peat as well as the rootlets of Ericaceae yielded Py-GC-MS traces with many aliphatic and alicyclic compounds and a large number of phenolic pyrolysis products derived from lignin. The suberin of the rootlets of Ericaceae is postulated to be an important source of aliphatic hydrocarbons, methylketones (C 17-C 31), unsaturated methylketones (C 19-C 29), 2,4-diketones (C 25-C 31), long-chain alcohols (C 15-C 25), fatty acids (C 8-C 24), 24-ethylcholesterol, 24-ethylcholestanol, 24-ethyl-cholestanone and a number of triterpenoids with friedooleanane skeletons (e.g. taraxerol and taraxerone). The presence in suberin of an insoluble aliphatic polymer, which is characterised by pyrolysate with alkane/alkene doublets ranging from C 6-C 33, is postulated.