Growth Characteristics and Freezing Tolerance of Ectomycorrhizal and Saprotrophic Fungi: Responses to Normal and Freezing Temperatures

In boreal and temperate forests, symbiotroph and saprotroph soil fungi must survive months of low temperatures or freezing during winter. In the temperate biome, this is particularly the case for high-elevation mountain forests. Soil freezing is thus an important stress factor in these forests. The objective of this study was to assess how temperature and freezing conditions affect the growth and survival of symbiotic and saprotrophic fungi. To assess the cold and freezing tolerance of ectomycorrhizal (EM) and saprotrophic (SAP) fungi, we conducted a study from 2021 to 2023, using isolates from forests located at lower and high-elevation mountain sites, as well as from forests in Mongolia, at altitudes ranging from 525 m to 1800 m. The isolates were grown in vitro at temperatures of 22, 15, and 4 degrees C and exposed to freezing conditions at -4 or -18 degrees C. The response to temperature and freezing was determined based on radial growth. Triphenyltetrazolium chloride (TTC) reduction was used to measure relative metabolic activity and viability. Fungi that originated from higher-elevation mountain sites, and thus colder climate conditions, tended to have a lower response to temperature and a higher tolerance to freezing. We could find no evidence of a higher freezing tolerance among different exploration types of ectomycorrhizal fungi. Sensitivity to low temperatures appears to be taxa-specific rather than exploration-type-specific.