Development of longitudinal split failure in white-rotted aspen (Populus tremuloides michx)

Abstract

Longitudinal splits and associated smooth fracture planes were often noted along the growth ring boundaries of aspen, Populus tremuloides Michx., which were impact-loaded on the tangential plane,after decay by Trametes versicolor (L.: Fr.) Pilat, and Bjerkandera adusta (Willd.: Fr.) Karst. To characterize this failure pattern, scanning (SEM) and transmission (TEM) electron microscopy were employed. Results showed that this failure is a result of longitudinal fracture lines that cut through the parenchyma cell-wall layers (transwall failure) and opened the lumens. These parenchyma cells were preferentially invaded by fungal hyphae early (weight loss = 10%) in the degradation process. Prominent on the fracture planes was evidence of parenchyma cross walls perpendicular to the fiber axis, fungal hyphae, and associated hyphal sheaths. Localized fracturing along the parenchyma cellssuggests that fungal invasion and degradation patterns influence the development and morphology of longitudinal fracture in wood.