Distribuição da lignina e variação do ângulo microfibrilar na parede celular em lenhos do fuste e galho de Hymenaea courbaril L.

Abstract

The generation of forest residues is an economic and environmental problem. Among the residues from Amazonian trees, the branches are the ones that present timber potential. The knowledge of the properties of wood branches, especially the microscopic characteristics, is still a bottleneck for some species from both planted forests and native forests of the Amazon region. Thus, the objective was to evaluate the spatial distribution of lignin and determine the variation of the microfibrillar angle in the cell walls of the stem and branch wood of Hymenaea courbaril L. as a contribution to the understanding of the alteration in the behavior of the reaction wood in relation to the normal wood. For this, two trees were collected, considering the upright trunk and the branches that had a minimum diameter of 30 cm. From each stem, a disc with a thickness of 10 cm in cross section was taken at a height of 1.30 m above ground level (diameter at breast height). A 10 cm thick disc was also removed from the base of each branch, totaling four discs used in the experiment. A 2-cm-thick central strip was removed from each disk for sample preparation. The samples were taken in three radial positions in the stem: internal, intermediate and close to the bark, in dimensions of 1 × 1 × 1 mm. The determination of the lignin distribution was carried out by means of Fluorescence Microscopy and the determination of the microfibrillar angle was performed by means of Transmission Electron Microscopy. There was no radial variation of lignin intensity in the pith-bark direction, for normal, opposed and tensile woods. Trunk wood had approximately 15% more lignin when compared to branch wood. Opposite wood had 31% more lignin when compared to tension wood. S2 layer was the thickest in the three types of wood, with an average of 2.19 μm in normal wood, 2.77 μm in opposite wood and 2.34 μm in tension wood; S3 layer, on the other hand, presented smaller averages, being 0.16 μm for the normal wood, 0.19 μm for the opposite wood and 0.23 μm for the tension wood; in layer S1 the values were 0.34μm for normal wood, 0.21 μm for opposite wood and 0.27 μm for tension wood; in the primary wall, the mean values obtained were 0.63 μm for normal wood, 0.39 μm for opposite wood and 0.61 μm for tension wood. The value average for the microfibrillar angle in layer S2 in normal wood 4.6°; opposite wood 2.8° and tension wood 4.3°. The images obtained did not allow us to determine the average values of microfibrillar angle in layers S1 and S3.