Fungi in the Arctic Environment
Fungi are heterotrophic organisms feeding by osmotrophy (see Intro to Fungi for a more general overview). Basically, their ecology can be divided into saprotrophs, parasites and mutualists. However, transitions exist between all these groups.
Most fungi in the arctic environment do also occur in alpine areas farther south, e.g. in the Scandinavian mountains and the Alps. Very few are restricted to the arctic areas. Fungi growing on arctic seashores, e.g. Arrhenia salina, are ecologically bound to the arctic zone. Some ectomycorrhizal fungi, as Lactarius lanceolatus, are more common in arctic than alpine sites. Some saprotrophic species, like Agaricus aristocratus, are hitherto only found in the Arctic, but since they are newly described species, often belonging to difficult genera, they may also show up in alpine areas if one seeks more thoroughly.
Fungi in arctic environments may experience frost nearly every day in the short growing season. Cold-tolerant organisms are called psychrophilic. One challenge for organisms in cold environments is the formation of ice crystals. A solution for most psychrophilic animals, plants and fungi to cope with the formation of ice crystals is the production of anti-freeze substances. For fungi, these can be proteins or alcohols of different kinds. Fungi produce these substances inside the hyphae to prevent their cells from freezing. In addition, they use the same substances to thaw the soil around them for mycelium growth and uptake of nutrition. These processes require energy, so most arctic fungi hibernate or grow slowly in temperatures below +5 ºC. In the Arctic, some specialised soil fungi can grow even in temperatures down to -2 ºC and tolerate heavy drought stress. Laboratory studies have shown that arctic fungi can survive temperatures below -100 ºC if they are surrounded by anti-freeze substances. However, this observation is only of theoretical interest, since in most arctic areas the ground is covered by insulating snow, preventing the ground from reaching temperatures as low as the air temperatures above. Soil-dwelling fungi benefit from this during the cold winter.
Another adaptation to low temperatures is the chemical composition of cell walls. Arctic fungi contain more unsaturated lipids than fungi farther south, and lower amounts of ergosterol (the fungal equivalent to cholesterol). Saturated lipids and ergosterol harden in low temperatures, which would make fungal cells stiff and brittle in cold conditions. Sometimes, only one of the two chemical adaptations is found. For example, the psychrophilic Mortierella elongata (Mucoromycota) showed absence of detectable ergosterol, but presence of the unsaturated stearidonic acid.