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/g uaiacyl (s/g) ratio, lignin content and polysaccharide composition (hexosan s/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 conten t 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 s tandard deviation was very high for the three determinations (2-3% coeffici ents of variation). Eccentric tree growth in E. globulus has no impact in t he s/g ratio and does not necessarily imply differences in lignin content o r in polysaccharide composition. When differences occur, lower lignin and h igher cellulose are found in the cross section part with the highest radial growth. Sampling for wood chemical analysis in eccentric cross sections sh ould avoid the stem parts with high radial differences between opposite sid es. Analytical pyrolysis can be used to prospect for the presence of tensio n wood. (C) 2001 Elsevier Science B.V. All rights reserved.