A COMBINED PYROLYSIS MASS-SPECTROMETRIC AND LIGHT-MICROSCOPIC STUDY OF PEATIFIED CALLUNA WOOD ISOLATED FROM RAISED BOG PEAT DEPOSITS

Stem wood of the Angiosperm Calluna vulgaris (Scotch heather), isolated at different depths from a selection of raised bog peat deposits, was chemically characterized using in-source pyrolysis mass spectrometry (Py-MS) and Curie-point pyrolysis gas chromatography mass spectrometry (Py-GC-MS). Light microscopy was performed to relate mass spectrometric characteristics with anatomical features. Peatifred wood samples, isolated from increasing depth show a gradual decrease in carbohydrate content. This decrease is anatomically reflected in a selective removal of secondary cell wall material from the fibre-tracheids and wood parenchyma. During prolonged peatification a selective removal of hemicellulose sugars is observed, while a part of the cellulose fraction is preserved. This highly resistant cellulose is mainly located in the secondary cell walls of the vessels. The lignin macromolecule is preserved, but a gradual decrease in springyl to guaiacyl ratio (S/G) is observed during peatification. Because no increase in catechol and phenolic compounds is observed, we conclude that S/G shifts are due to the removal of syringyl-rich secondary cell wall material and the retention of guaiacyl-rich compound middle lamella. Small chemical changes in the lignin macromolecule involve shifts in oxygen substitutions on the aliphatic side chains of the methoxyphenolics and the occurrence of aromatic acids.