Influence of tree eccentric growth on syringyl/guaiacyl ratio in Eucalyptus globulus wood lignin assessed by analytical pyrolysis

Wood disks from 9-year-old Eucalyptus globulus trees that showed eccentric growth were analysed by analytical pyrolysis to determine lignin syringyl/guaiacyl (s/g) ratio, lignin content and polysaccharide composition (hexosans/hexosans + pentosans). Three cross-sectional fractions were analysed: the long radius, the short radius and the intermediate sections. Between-tree variation was observed for the s/g ratio from 2.0 to 2.8, the lignin content from 26.5 to 28.0% and the hesosans/hexosans + pentosans ratio from 0.76 to 0.83. The reliability of the pyrolysis analysis assessed by the pooled standard deviation was very high for the three determinations (2-3% coefficients of variation). Eccentric tree growth in E. globulus has no impact in the s/g ratio and does not necessarily imply differences in lignin content or in polysaccharide composition. When differences occur, lower lignin and higher cellulose are found in the cross section part with the highest radial growth. Sampling for wood chemical analysis in eccentric cross sections should avoid the stem parts with high radial differences between opposite sides. Analytical pyrolysis can be used to prospect for the presence of tension wood. (C) 2001 Elsevier Science B.V. All rights reserved.