Fungi growing in liquid culture undergoes three separate phases in which they i) adapt to the new environment, ii) grow unrestrictedly and exponentially, and iii) are inhibited to increase in number/mass due to lack of nutrients etc. Filamentous fungi have been shown to exhibit similar growth phases in a solid food substrate and have been modelled to grow in this way also in solid wood. In modified wood with high treatment levels, fungi cause no or little mass loss but the reason for this has not been fully explained. To be able to predict the service-life of modified wood, understanding the growth pattern of wood degrading fungi in these materials may be important. The aim of this study was to find out whether brown rot fungi undergoes the same growth phases in solid wood as in liquid culture and study the growth pattern of brown rot fungi in modified wood. This was done through high-frequent monitoring of mass loss over 300 days of exposure of acetylated and furfurylated wood to Postia placenta. Mass loss results of the untreated wood indicated clearly that the fungi in this material go through phases similar to phases seen in liquid cultures. However, the results for the modified wood materials were less clear. Little mass loss and a degradation rate 100 times lower than in the untreated wood during exponential growth may suggest that the fungi in the modified wood samples were still adapting to the new environment. On the other hand, the fact that mass was lost at all suggests that degradation did occur and that the fungi were growing exponentially.

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