Interactions Between Temperature Moisture and Fungi Indoors

Although little is known regarding interactions between temperature (T ), moisture, and fungi in the indoor environment, studies on the interactions in the environment offer some useful information.

Although relative humidity (RH) and temperature were reported to be the most important environmental parameters regulating spore production,54'55 current understanding of the relation between fungal growth and the availability of free water (aw) in the growth substrate have significantly changed the importance of RH on spore production. Sufficient moisture is not only important in vegetative growth but also the most important factor in sporulation.48 Spore release and dispersal of some hyphomycetes was correlated with increasing T and decreasing RH. Lower RH allows dry spores to become airborne. The moisture content of the indoor air was reported to have significant effects on all measurable airborne spore concentrations.56 Spore release of Botrytis squamosa, which is most likely of outdoor origin, was promoted largely by declining RH, increasing T, and rain, but occasionally by increased RH.46 On the other hand, Leach49 found that spore release of Drechslera turcica and several other fungi was affected by decreasing RH but not by temperature changes. Drastic increases of conidia of Cercospora asparagi were trapped beginning at 7:00-8:00 a.m., when T increased and RH fell below 90%.57 Beaumont et al.58 reported a positive correlation between concentrations of total airborne spores of Cladosporium and Botrytis with higher temperatures.

Variations and fluctuations in indoor humidity and temperature were found to have significant effects on fungal growth,33,59 such as in a bathroom situation with transient high humidities where dominant mycota included species of Alternaria, Aureobasidium, Cladosporium, Phoma, and Ulocladium.25,60

Basidiospores of Paxillus panuoides Fr., a mushroom likely found outdoors, were released when temperatures were above freezing, and daily peaks were usually correlated with increased T and decreased RH. Spore releases were found to increase from a temperature of 2°C, to a maximum at 37°C, but ceased at 45°C. RH treatments did not significantly affect spore release. Temperature was determined to be the stimulus for the natural spore release pattern.61 Higher counts of basidiospores might be due to higher relative humidity and lower sunshine in 1978 in Galway, Ireland.62 Li63 found that RH and dew were positively correlated with release of basidiospores of Amanita muscaria var. alba, and T values showed no significant correlation with the release of the basidiospores. Less than 0.1% of the basidiospores released infiltrated a residence nearby. Because fluctuations and changes of RH are related to temperature variations as well as moisture sources, the effects of these two parameters could not be defined independently.

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