X-ray diffraction (XRD) is based on the creation of an interference pattern by x-rays when they encounter a regularly spaced matrix. In wood, this process has been used to determine, among other things, the average width of the cellulose microcrystals, the percent of crystalline cellulose within the wood, and can be used to examine the changes in these parameters during degradation. Enhanced understanding of the mechanisms and effects of wood degradation through x-ray diffraction may improve knowledge of degradative processes and facilitate the development of more effective decay prevention measures. Studies were conducted to determine changes over time in wood crystallinity generated by the brown rot fungus Meruliporia incrassata and the soft rot fungus Chaetomium elatum. Fungi were grown in modified soil block jars with spruce wood blocks for 2, 4, 6, and 8 weeks. After removal from the jars, wood blocks were dried, analyzed for weight loss, ground into powder, and pressed into pellets. Pellets were analyzed by x-ray diffraction using a ?-2? scan and the resulting spectra were deconvoluted to determine average crystallite width and overall percent crystallinity. Results showed an increase in crystallite width by M. incrassata by the fourth week of decay, followed by a slow decrease. Percent crystallinity values showed an increase at 2 weeks of decay followed by a gradual decrease. There were only minor differences between C. elatum and the controls in both crystallite width and percent crystallinity over the four time periods.

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