Changes in wood microstructure through progressive stages of decay

Abstract

Successive stages of decay in the sapwood of sweetgum (Liquidambar styraciflua L.), a hardwood, and of southern pine (Pinus sp.), a softwood, were observed microscopically. The white-rot fungus. Polyporus versicolor L., and the brown-rot fungus, Poria monticola Murr., were the fungi used or the observations, light microscopy, plus the techniques of polarization and ultraviolet-absorption microscopy, was used on sections 4 microns thick cut from celloidin-embedded specimens. For both fungi, hyphae were widespread in the early stages of decay in both types of wood. The hyphae of the white rotter were much more numerous than were those of the brown rotter. The white-rot fungus in penetrating the cell walls went through both pits and numerous bore holes: the brown-rot fungus penetrated pits almost exclusively. Pit canals were enlarged by both fungi to the extent that they could not be distinguished from true bore holes in any but the early stages of decay. Results indicated that the action of the cellulolytic enzymes of the white-rot fungus was restricted to the cell wall surfaces, whereas the cellulolytic enzymes of the brown-rot fungus and the lignin-destroying enzymes of the white-rot fungus were able to penetrate and act within the cell wall. The resistance of the cell walls to brown rot was positively correlated with the lignin content. Essentially all loss in weight of wood could be accounted for by microscopically visible loss of cell wall substance.

Citation

Wilcox, W. Wayne. 1968. Changes in wood microstructure through progressive stages of decay. Research paper FPL no. 70. Madison, WI : USDA, Forest Service, Forest Products Laboratory. 45 pages.