Removal of Lignin from Partially Delignified Softwoods by Soft Rot- and White Rot Fungi

Abstract

The pattern of lignin removal from partially delignified woods by a soft rot fungus (Chaetomium globosum KUNZE) and a white rot fungus (Coriolus versicolor QUEL.) has been studied on two softwoods (Pinus densiflora SIEB. et Zucc. and Cryptomeria japonica D. DON) and one hardwood (Fagus crenata BLUME), with reference to the different acceleration pattern of wood decay caused by the partial delignification. The rapid and shorter acceleration, which was observed for the cases of P. densiflora and C. japonica attacked by Ch. globosum and Co. versicolor, respectively, was accompanied with the rapid rate of lignin removal and the higher ratio of lignin loss to weight loss at smaller extent of delignification. The slow and longer acceleration, for the cases of P. densiflora and C. japonica attacked by Co. versicolor and Ch. globosum, respectively, was accompanied with the slow or poor overall removal of lignin. In the former case, the lignin was removed apparently at slower rate than non-lignin components, and removal or modification of lignin probably acts largely for facilitating fungal enzyme systems to gain access to the carbohydrates. In the latter case, the ratio of lignin loss to weight loss increased in proportion to the extent of delignification and reached the maximum level at the moderate extent of delignification. In the case of F. crenata which has high susceptibility to both fungi, the rate of lignin removal and the ratio of lignin loss to weight loss were always slower and smaller in Ch. globosum than in Co. versicolor.