Wood decaying fungi are an essential part of any ecosystems as they are the main decomposers of cellulose and lignin-containing materials. But as wood is a common building material the risk for decay fungi growth and subsequent degradation of our construction material is a concern. There are important physiological aspects of the growth and activity of decay fungi that are unknown today, and without knowledge on these factors it is not possible to make physiological relevant models for decay fungi. Measurements of heat production rate have been made with isothermal calorimetry on wood samples with the brown rot fungus Postia placenta at different moisture contents. Isothermal calorimetry gives a direct measurement of an organism’s activity as it measures the heat produced when the organism respires and it is has shown to be a very suitable method to study fungal activity as a function of different parameters. The results clearly show the heat production rate (a measure of respiration rate and fungal activity) is moisture dependent. For most cases, less heat was produced when the moisture content was decreased, and more heat was produced when the moisture content was increased. It was also found that when the moisture content increased after a dry period, the increase in activity was significantly delayed. However, if the moisture state was then kept constant at a high level the activity slowly increased, showing that the fungi need time to recover back to the original activity level after drying. Isothermal calorimetry is a measurement technique well suited for the study of the activity of wood-decaying fungi as a function of temperature and moisture content.

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