On the changes of pinewood ( Pinus sylvestris L.) Chemical composition and ultrastructure during the attack by brown-rot fungi Postia placenta and Coniophora puteana

Pine sapwood blocks were exposed to brown-rot fungi Postia placenta and Coniophora puteana for 1, 2, 3, and 4 months. Ion exchange chromatography method was used to determine the changes in sugar content during brown-rot decay. The most remarkable feature was the preferred degradation of mannose both by P. placenta (80.9% weight loss) and C. puteana (77.5% weight loss) in comparison to the control. It can be interpreted as a result of the preferred degradation of the backbone chains of O-acetyl-galacto-glucomannans. For scanning electron microscopy, the wood degradation sequences obtained by the fracture method were used. The fractured surface of cell wall reflected the pattern of degradation of cellulose microfibrils. The surface of secondary wall decayed by P. placenta revealed both smooth and uneven regions throughout the test. C. puteana retained uneven cell wall surface only after the first month, while later the surface became smooth. This suggests that P. placenta tended to degrade cellulose amorphous regions more readily, while C. puteana, possessing full enzyme complement, was able to degrade both amorphous and crystalline regions more readily. The water vapor sorption method was applied for microstructural characteristics of wood. The formation of new pores of size 2.1–9.9 nm occurred during brown-rot decay, whose sizes and volume depend on the fungus culture and exposure time. It is assumed that the appearance of these pores is caused by the destruction of carbohydrates.