Anatomy of bioincised Norway spruce wood

Bioincising is a biotechnological method to enhance the permeability of refractory wood species such as Norway spruce (Picea abies (L.) Karst) by incubation with the white rot fungus Physisporinus vitreus. Increase in wood permeability is supposedly induced by the selective degradation of pit membranes in the bordered and half bordered pits, entailing only negligible changes in the tracheid cell wall. In order to analyze the fungal activity on pit elements and the cell wall structure, we incubated sap- and heartwood of Norway spruce for three, five, seven and nine weeks with P. vitreus. After incubation and wood sterilization we conducted a systematic microscopic study. We found that P. vitreus caused both a selective delignification and a soft rot Type I and II in tracheid cell walls comprising a high heterogeneity during wood colonization. Moreover it was apparent that the degradation of pit membranes occurred simultaneously with the formation of bore holes, cavities and notches in tracheid cell walls. The activity of P. vitreus was higher in the sapwood, but a notable effect was also recorded in the heartwood. The results indicate that the incubation conditions have to be further optimized to reduce the adverse effects of fungal activity on the tracheid cell walls and achieve a more homogenous wood colonization. The results of this study help to improve the bioincising process by understanding the growth characteristics of P. vitreus and the wood-fungus interaction during wood decay.