We studied the effect of decay on the water adsorption capacity and the concentration of extractives of Scots pine (Pinus sylvestris L.) heartwood by comparing corresponding properties of decayed and intact wood blocks. The samples derived from 39 even-aged trees having a large between-tree variation in the extractive concentrations, and subsequently in the mass loss in the brown-rot (Coniophora puteana) decay test. The water adsorption capacity was measured at a high relative humidity (RH ~100 %, 21ºC). In contrast to expected, the equilibrium moisture content (EMC) of brow-rotted heartwood appeared to be significantly higher than that of undecayed heartwood. We explained this result by the increased capacity for capillary condensation. The chemical composition of heartwood was changed radically by the brown-rot fungus. The concentration of stilbenes, resin acids and free fatty acids decreased indicating that the fungus was able to eliminate the extractives at a faster rate than cell wall constituents. At the same time the concentration of total phenolics increased which obviously reflected changes in the chemical structure of the main cell wall constituents. Also the concentration of soluble sugars increased as a result of decay, and in addition, fungal sugars were found in the decayed samples. As one conclusion, the high hygroscopicity of brown-rotted wood should be taken into account e.g. when carrying out repairs on buildings damaged by advanced decay.
Keywords: brown-rot decay, extractives, Scots pine heartwood
Authors
Martti Venäläinen
Finnish Forest Research Institute, Punkaharju Research Unit, Punkaharju, Finland
Anni Harju
Finnish Forest Research Institute, Vantaa Research Unit, Vantaa, Finland
Tapio Laakso
Finnish Forest Research Institute, Punkaharju Research Unit, Punkaharju, Finland
Outi Karppanen
Finnish Forest Research Institute, Punkaharju Research Unit, Punkaharju, Finland
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