Arboriculture & Urban Forestry 36(3): March 2010 test. Thus, the difference in the weight loss in wood decayed by F. palustris and T. versicolor might have been affected by the agar medium in the present study. On the other hand, in the soft rot fungus, nearly the same values in weight loss ratio were observed throughout the decay period, indicating the soft rot fungus did not decay the specimens as severely as the other two fungi did during the 60-day period. A soft rot fungus generally shows strong decay ability under very wet conditions. In the present study, the relative humidity in the incubator chamber was not controlled through the test period. Therefore, the weight loss ratio was considered low. Wood decayed by brown rot fungi becomes brittle and friable, while when decayed by white rot fungi retains much of its strength even at fairly advanced stages of decay (Kollmann and Côté 1984; Schwarze et al. 2000; Schmidt 2006). Time-course changes of CS are shown in Figure 3. Before the decay test, the CS was 24.3 MPa, but it decreased to about 20 MPa within 15 days of decay in all specimens. In brown rot and white rot fungi, nearly constant CS values were found from 15 days to 45 days of decay. However, the CS values decreased markedly on the 60th day: the CS values of specimens decayed by brown rot and white rot fungi were 13.3 and 8.8 MPa, respectively. On the other hand, in soft rot fungi, the CS values were nearly constant from 15 to 60 days of decay. Figure 4 shows time-course changes in the chemical compo- nents of wood core samples due to decay by three fungi. The contents of holocellulose, Klason lignin, and α-cellulose in non- decayed specimens were 77.6%, 21.5%, and 43.4%, respectively. After 60 days of decay, the contents of wood decayed by brown rot fungus were 51%, 18.2%, and 23.5%, respectively, indicating that the carbohydrate fraction was markedly decomposed by the brown rot fungus. Fukuda and Haraguchi (1974) reported that the contents of holocellulose markedly decreased in wood de- cayed by F. palustris compared to sound wood. The results ob- tained for brown rot were similar to those reported by Fukuda and Haraguchi (1974). On the other hand, the contents of wood decayed by the white rot fungus decreased at almost the same rate throughout the decay period. In addition, the fact that weight loss 83 occurred in wood decayed by the white rot fungus suggests that the wood components were significantly decomposed. In general, white rot fungi decompose cellulose, hemicellulose, and lignin at the same rate (Kollmann and Côté 1984; Schwarze et al. 2000; Schmidt 2006); therefore, these contents showed almost constant rates through the decay period. On the other hand, throughout the decay period, nearly the same contents of holocellulose, Klason lignin, and α-cellulose were found in wood decayed by the soft rot fungus. This tendency was similar to the results ob- tained for the weight loss of wood decayed by the soft rot fungus. Figure 2. Time-course changes in weight loss of wood core sam- ples of Magnolia obovata. Bars indicate standard deviation. The mean values followed by the different letter indicate significant difference (P > 0.05) among the three types of fungi at the same culture period by the Tukey’s HSD test. Figure 3. Time-course changes in Fractometer-measured com- pressive strength in Magnolia obovata. Bars indicate standard deviation. The mean values followed by the different letter indi- cate significant difference (P > 0.05) among the different decay period of a fungus by the Tukey’s HSD test. ©2010 International Society of Arboriculture
March 2010
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