Py–GC/MS study of Eucalyptus globulus wood treated with different fungi

Abstract

The degradation patterns of Eucalyptus globulus wood by several wood-rotting fungi from the groups of ascomycetes, basidiomycetes and deuteromycetes were studied by analytical pyrolysis coupled to gas chromatography/mass spectrometry. The pyrograms of sound and degraded eucalypt wood showed several major peaks from lignin breakdown, identified as guaiacol, 4-methylguaiacol, 4-vinylguaiacol, eugenol, syringol, trans-isoeugenol, 4-methylsyringol, 4-ethylsyringol, 4-vinylsyringol, 4-allylsyringol, syringaldehyde, trans-4-propenylsyringol, acetosyringone, syringylacetone and propiosyringone. Products arising from carbohydrate pyrolysis could also be recognized. Similar pyrolysis compounds were found during analysis of sound and decayed wood, but differences were observed in their relative abundances. Relative peak areas were calculated for guaiacyl (G) and syringyl-type (S) lignin breakdown products, as well as for compounds arising from carbohydrates. Several basidiomycetes were found to be the most efficient lignin degraders on eucalypt wood as revealed by lignin/carbohydrate ratio from pyrolysis products. Among them, Poria subvermispora caused the most intense removal of lignin moiety from eucalypt wood. A decrease of lignin S/G ratio was observed during wood delignification, the lowest ratio being found also in the wood treated with P. subvermispora. This is due to the preferential biodegradation of ether-linked S-lignin yielding a residue enriched in G-lignin that is more recalcitrant towards fungal attack because of its higher condensation degree. On the other hand, deuteromycetes preferentially degraded the carbohydrate moiety while the ascomycetes included in this study did not show any particular preference in the degradation of eucalypt wood constituents.