Abstract
The heartwoods of many wood species have natural resistance to wood decay due to the accumulation of antifungal heartwood extractives. The natural durability of heartwoods has been extensively investigated, yet very little information is available on the initiation of heartwood decay. This experiment examined the onset of Rhodonia placenta brown rot decay in Scots pine heartwood in order to identify the key changes leading to heartwood decay. An imaging approach based on Raman imaging and multivariate image analysis revealed that the degradation of heartwood began in the innermost cell wall layers and then spread into the remaining cell walls and the middle lamella. Pinosylvins were extensively degraded in the cell walls, middle lamella and extractive deposits, while unidentified material most likely consisting of hemicelluloses and/or lipophilic extractives was removed from the inner cell wall layers. Changes similar to inner cell wall degradation were seen in the remaining cell walls in more advanced decay. The results indicate that the key change in incipient heartwood decay is the degradation of antifungal heartwood extractives. The inner cell wall degradation seen in this experiment may serve a nutritive purpose or facilitate the penetration of degradative agents into the cell walls and middle lamella.
Highlights
Wood decay is a process in which specialised wood decaying fungi degrade and consume the polymeric constituents of wood
The use of principal component analysis (PCA) and pixel clustering with Raman imaging improved the sensitivity of the method and made it possible to detect the slight spectral alterations caused by incipient decay
This work investigated the incipient stages of brown rot decay in Scots pine heartwood in order to identify the key steps in heartwood degradation
Summary
Wood decay is a process in which specialised wood decaying fungi degrade and consume the polymeric constituents of wood. The sapwoods of most wood species are quite susceptible to decay, but many species produce heartwood that can have varying levels of natural decay resistance. The heartwoods of many wood species have been characterised in terms of their decay resistance, and the composition and properties of their extractives have been extensively investigated[2,3,4,5]. In northern Europe, Scots pine (Pinus sylvestris L.) is the most widely available wood species that produces naturally decay resistant heartwood. With information on heartwood decay lacking, this experiment investigated how the chemical composition of Scots pine heartwood changes during the initial stages of brown rot decay. The cellular level distributions of these changes were analysed by confocal Raman spectroscopy imaging in combination with principal component analysis (PCA) and cluster analysis. The use of PCA and pixel clustering with Raman imaging improved the sensitivity of the method and made it possible to detect the slight spectral alterations caused by incipient decay
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