Lignin Distribution in Wood Delignified by White-Rot Fungi: X-Ray Microanalysis of Decayed Wood Treated with Bromine

Lignin concentration was determined in cell wall layers of sound and white-rotted birch and pine wood using energy dispersive X-ray analysis. Two types of selective lignin removal were identified. In one type, characteristic of Phellinus pini decay, lignin was completely removed from all cell wall layers, but only in localized areas of wood blocks. In the other type, characteristic of Pholiota mutabilis and Phanerochaete chrysosporium decay, extensive amounts of lignin were uniformly removed from wood blocks, but the major attack occurred in the S₂ layer of fiber cell walls with virtually no degradation of cell corners. Phlebia subserialis, a non-selective lignin degrading fungus, removed similar amounts of lignin from wood blocks as Phell. pini and Phol. mutabilis, but complete dissolution of all cell wall components occurred where lignin was degraded. The process of lignin removal from wood cell walls, whether selective or not, varies among white rot basidiomycetes.