Qualidade dos lenhos normal e de reação de Eucalyptus urophylla x Eucalyptus grandis por meio de técnicas microscópicas e espectroscópica

Abstract

Trees subjected to adverse environmental conditions tend to develop reaction wood, characterized by structural and chemical modifications in the cell wall that may influence its technological properties. In this context, the aim of this study was to evaluate the structure and chemical composition of the cell wall of wood from vertical and inclined trees of a 7-year-old clone of Eucalyptus urophylla × Eucalyptus grandis using Confocal Raman Microscopy (CRM) and Atomic Force Microscopy (AFM). Five vertical trees and five inclined trees were evaluated. Initially, biometric measurements and Residual Longitudinal Strain (RLS) were performed. After harvesting, 3-m-long logs were collected to obtain discs for pith eccentricity determination and samples for anatomical and ultrastructural analyses. Fiber biometry, microfibril angle (MFA), cell wall chemical mapping by CRM, and cell wall imaging by AFM were assessed. Inclined trees showed higher RLS values than vertical trees, indicating the presence of reaction wood and greater growth stresses. No significant differences were observed in pith eccentricity between the evaluated groups. Fiber dimensions increased from pith to bark, whereas MFA showed a decreasing trend along the same radial direction. Normal wood exhibited longer fibers, while tension wood presented thicker cell walls, particularly in the outer region of the stem, as well as higher MFA values. Cell wall chemical mapping by CRM revealed an increase in lignin concentration from pith to bark, with higher intensities associated with Raman bands near 1600 cm⁻¹, especially in the middle lamella and cell corners. Bands attributed to cellulose, near 380 cm⁻¹, were identified in the average spectra of normal, tension, and opposite wood at both radial positions. Tension wood exhibited lower relative intensity of the lignin band compared with the other wood types. AFM imaging allowed the distinction of cell wall layers, although without complete visualization of the microfibrillar organization.