Date of Award

12-2008

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Botany and Plant Pathology

Advisor

Jody Jellison

Second Committee Member

Barry Goodell

Third Committee Member

David Neivandt

Abstract

The mechanisms involved in fungal biodegradation of wood have been studied intensively for many years due to their relevance to both preservation of in-service wood and to nutrient cycling in forest ecosystems. The purpose of this work was to further the understanding of the mechanisms and processes involved in fungal degradation of wood by using X-ray diffraction (XRD) to characterize nanoscale changes in wood crystalline cellulose. Wood degraded by four isolates of brown rot fungi was examined for changes using XRD. All fungi tested depleted amorphous materials thereby increasing the the apparent percent crystallinity early in the decay process. The total amounts of crystalline and amorphous material were reduced during the decay process. Data also showed a decrease of approximately 0.05 A in the average spacing of the crystal planes after approximately 20% weight loss. This may be due to the disruption of the outermost semi-crystalline chains in the cellulose microfibrils or elementary fibrils. Biomimetic tests designed to chemically simulate non-enzymatic decay yielded no repeatable significant differences relative to controls, indicating that perhaps XRD may not be sensitive enough to detect the types of changes caused by this system, or that the biomimetic system had not been optimized, or that the system used is not effective in attacking cellulose. Tests designed to simulate the removal of hemicelluloses early in the decay process using a hot water extraction procedure yielded results similar to those observed in wood in the early stages of decay by brown rot fungi with regard to X-ray diffraction patterns. These results may indicate that a portion of the hemicellulose contributes to the crystallinity of wood or that different methods of removing hemicelluloses have a similar effect on the crystallinity of cellulose. Wood -polymer composites treated with hot water hemicellulose extraction were subjected to decay by five species of brown rot and five species of white rot fungi. There were no significant differences in decay between extracted and non-extracted wood for the brown rot fungi tested, however the white rot fungi tested decayed the extracted wood significantly less than the untreated wood. These results indicate that the wood modified in this fashion does not obviously alter the macroscopic pattern of decay for the brown rot fungi tested, and appears to limit decay by the white rot fungi tested, possibly due to the different methods of decay used by these two groups. Overall, these studies suggest that wood degrading fungi alter wood crystalline cellulosic nanostructures early in the decay process, and that this is likely associated with the early removal of hemicelluloses as well as changes in the cellulose structures and composition. Furthermore, these studies suggest that artificial modification of the wood crystalline cellulose nanostructures through removal of hemicelluloses has a significant effect on white rot fungi, but not brown rot fungi. Additionally, this work establishes XRD as a tool for the characterization of wood crystalline cellulose nanostructures and may facilitate the use of this methodology to answer emerging questions in the area of wood biodegradation.

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