Intra-ring checking in Pinus radiata D. Don: the occurrence of cell wall fracture, cell collapse, and lignin distribution.

摘要

Ultrastructural and cytochemical features of tracheid cell walls were examined in oven-dried Pinus radiata D. Don disks that demonstrated a range in severity of the wood quality flaw referred to as "intra-ring checking," from severe to none. Observations of the tracheid cell wall at the ultrastructural level included the localization of the origin of tears between adjacent cells, and the occurrence of tracheid collapse. Cytochemical analysis focused on determination of the spatial distribution of lignin within the cell wall layers. Tracheid lignin content was further quantified using the Klason and acetyl bromide methods. We found considerable homogeneity in the point of failure in the wood demonstrating intra-ring checking, with 80% of the tears occurring at the compound middle lamella (CML)/S₁ cell wall interface. In these samples, tracheid collapse was observed adjacent to the tear as well as between tears, and the cell walls appeared to have altered lignin distribution, particularly in the S₁ wall layer. We suggest that alterations in the CML/S₁ layers create a weak point in the cell wall, making it prone to the observed tears. The mechanisms that may be involved in the occurrence of intra-ring checking are discussed at the morphological level.