Effect of Physisporinus vitreus on wood properties of Norway spruce. Part 1: Aspects of delignification and surface hardness

Abstract

The white rot fungus Physisporinus vitreus is currently tested for several biotechnological applications such as permeability improvement of refractory wood species or the optimization of the acoustic properties of wood for violins. The enzymatic activity of P. vitreus results in the degradation of pit membranes and simultaneous alterations of the tracheid cell wall structure in wood of Norway spruce wPicea abies (L.) Karstx. By this means, selective delignification and simultaneous degradation occur in the latewood tracheids at short incubation times. To study the delignification of individual cell wall layers in latewood tracheids, cellular UVmicrospectrophotometry was applied to wood of Norway spruce that had been incubated for between 3 and 9 weeks. By means of this technique, the progressing delignification was demonstrated in the latewood tracheid secondary walls. Moreover, local delignification in close proximity to hyphal tunneling, cavities, and notches was evident. Additionally, the mechanical changes were measured (a) at the macroscopic level by Brinell hardness test and (b) at the cellular level by nanoindentation. Brinell hardness was significantly reduced with increasing incubation time which was attributed to the partial delignification. Unlike Brinell tests, results from nanoindentation tests did not show a clear effect of fungal activity because of the material heterogeneity and the high spatial resolution of this technique. The present study provides methodological approaches for the investigation of wood-fungus interactions and contributes to a better understanding of the characteristics of wood decay at the subcellular level caused by the white rot fungus P. vitreus. Moreover, it establishes the basis for a subsequent chemical analysis, for which the results will be the topic of a second paper in this series.

Effect of Physisporinus vitreus on wood properties of Norway spruce. Part 2: Aspects of microtensile strength and chemical changes

“…After sterilization, the specimens were incubated with the white rot fungus P. vitreus for 3, 5, 7, and 9 weeks at 228C and 70% RH. For a detailed description of material selection and specimen preparation, see Lehringer et al (2011). Density and mass loss were calculated as described in Lehringer et al (2010).…”

“…Chemical analysis was conducted on smaller wood specimens of Norway spruce SW and HW (L=R=Ts100=15=10 mm 3 ) that were incubated separately, but exactly following the same incubation routine as used for the larger specimens in Lehringer et al (2011). Three replicates for each incubation time were prepared.…”

“…Analysis of Brinell hardness revealed a significant hardness reduction in the subsurface area after 7 and 9 weeks incubation (Lehringer et al 2011). In the same work, the application of cellular UV-microspectrophotometry (UMSP) indicated chemical alterations of the main wood components in close vicinity of fungal hyphae.…”

“…wood by means of a biotechnological method called ''bioincising'' has been investigated intensively during the past years (Schwarze and Landmesser 2000;Schwarze et al 2006;Schubert et al 2009;Schwarze and Schubert 2009;Lehringer et al 2010;Lehringer et al 2011). Hereby, the white rot fungus Physisporinus vitreus is supposed to selectively degrade the membranes of the bordered and half-bordered pits during short-term incubation times.…”

Penetration capacity of the wood-decay fungus Physisporinus vitreus

“…This biotechnological process, which is termed bioincising, can be used to improve the uptake of wood preservatives and wood modification substances Schwarze & Schubert 2011). In this context several studies concerning P. vitreus addressed the anatomy of treated Norway spruce wood (Fuhr et al 2011a;Lehringer et al 2010;Stührk et al 2010;Fuhr et al 2012), the influence of environmental factors to its radial growth rate (Fuhr et al 2011b;Schubert et al 2010) and the alteration of wood properties Schwarze et al 2008;Lehringer et al 2011a;Lehringer et al 2011b). Despite their potential, the methods mentioned are unable to illustrate the influence of microscopic effects such as the pit degradation rate on the macroscopic behavior of the fungus, because wood is an opaque material and the in vivo observation of processes inside a wood sample has not been possible until now.…”