Fungi in the Arctic – diversity of species and adaptation to cold climate
All terrestrial ecosystems have a high, and largely unknown, species richness of fungi. It is estimated that 1.5 million species of fungi exist on earth. Fungi are the most species rich group of organisms after insects. The overwhelming majority of these remain to be discovered, a mere five percent of them are known to science. This is particularly true for cold dominated ecosystems in the Arctic and Antarctic, where few mycologists have explored. Accordingly, knowledge of the ecology of Arctic fungi, the conditions they require, their ecological adaptations and roles is almost non-existent.
Arctic fungi – omnipresent but generally invisible
Fungi are commonly overlooked as both their presence and activities are largely invisible. The fungal cells, hyphae and mycelia, grow abundantly everywhere where organic material is present. The density of active hyphae is often hundreds of metres per gram of organic soil or plant litter. Their presence is often overlooked as the hyphal diameter is microscopic, a few thousand of a millimetre, and they grow in opaque substrate. The production of fungal sporocarps, their obvious manifestation, is strongly controlled by climatic factors and thereby erratic and varies considerably from year to year. Even more importantly, analyses over the last decade have excitingly shown sporocarps to be a poor indicator of the presence of fungal species and their activities. Many fungal species either lack sporocarps, only produce inconspicuous and ephemeral sporocarps or only rarely fruit in specific conditions. For example, in boreal forest soil, the overwhelming part of fungal diversity and activities is conducted by species never or rarely encountered as sporocarps. In cold-dominated environments, the discrepancy between the fungal community as reflected by sporocarps and the fungal community in soil is considered as even greater.
Adopted for clonality and longevity
Soil-dwelling fungi are clonal and grow by mycelial extension. Potentially, individual mycelia have indeterminate growth and age. The Arctic environment probably opts for traits such as longevity and mycelial spread of individual fungal mycelia. New colonization from spores may thus be extremely rare events. The fungi have these sets of traits or adaptations to the conditions of the Arctic environment largely in common with the Arctic plants.
Ecological roles of fungi
Fungal activities are of paramount importance in Arctic ecosystems as in all terrestrial ecosystems. In principle, all decomposition of dead organic material, particularly plant remains, is conducted by fungi, which thereby are critical for the recycling of nutrients. In addition, almost all plants live with an intimate and mutualistic relationship with fungi: a symbiosis known as mycorrhiza. The fungal hyphae, and the cells in the plant’s fine root, form an integrated unit called mycorrhizal root. At this connection, the fungal hyphae provide the plant with nutrients while the fungus receives sugar from the plant. Different groups of plants form this obligate mycorrhizal symbioses with different sets of fungi. Whereas all woody plants in the Arctic form mycorrhiza (ecto-) with fungi that we commonly encounter as sporocarps such as boletes and chanterelles, ericaceous plants and herbs form mycorrhiza (ericoid- and arbuscular mycorrhiza, respectively) with fungi lacking sporocarps.
The amount of energy, or assimilate from the photosynthesis, translocated to the mycorrhizal fungus from the mycorrhizal plant is considerable, ranging from 15–25 percent of the plant’s netphotosynthesis (netphotosynthesis =the plant’s total photosynthesis minus the energy used by the plant for its respiration). In comparison, herbivores typically graze 5-10 percent of the above ground biomass of plant communities. Importantly, fungal soil hyphae constitute the basis for the food-webs in soil, as most soil animals, i.e. collembolas, are fungivores and graze hyphae.
Unique fungal samples during Tundra Northwest 1999
The Tundra Northwest 1999, enabled this project to explore mycorrhizal fungi in the Arctic by collecting unique and generally inaccessible root and soil samples. A unique feature of the Arctic tundra is that non-mycorrhizal plants are widespread and predominate in certain plant communities over large areas. Ectomycorrhizal fungi are present as symbionts of a relatively few common and widely distributed shrubs, willows (Salix spp) and mountain avens (Dryas). Arbuscular mycorrhizal fungi are ubiquitous in the low Arctic but are rare or non-existent in the High Arctic. Physical environmental features strongly limit and shape the species diversity of fungi in the Arctic.
Aims – assessment of fungal diversity and physiological adaptation
The primary aim of this project was to identify which fungal species form Ectomycorrhizal symbios with the two most abundant and widely spread Ectomycorrhizal plants in the Arctic; Salix arctica and Dryas integrifolia. Our aims also include examining how the last glaciation and environmental settings have shaped species diversity at different spatial scales. These analyses are integrated with the distribution analyses of plants, lichens and mosses. We will also investigate whether S. arctic a and D. integrifolia, at least in part, may be colonized by the same set of Ectomycorrhizal fungal species. If this is the case, these two plant species, which commonly grow closely intermingled, may be physically and physiologically interconnected by common mycelia. This has been found in other ecosystems and affects competition between the plants.
The secondary aim of the fungal project was to search for physiological adaptation of Arbuscular mycorrhizal fungi in these cold-dominated environments. Possibly, the membranes of these fungi have a lipid composition that allows them to function at low temperatures. We thus collected soil and roots from plants that potentially host Arbuscular mycorrhizal fungi from sites in the High Arctic. Back in Sweden, the aim is to compare the physiology, particularly the membrane lipid composition, of fungi from the Arctic with fungi from temperate areas.
DNA-fingerprinting analyses of 1600 mycorrhizal roots
As sporocarps are poor indicators of the presence of fungal species and their abundance, root samples of Arctic willow (S. Arctica) and mountain avens (D. integrifolia) were collected. These root samples were washed at the boat and samples of individual fine roots with Ectomycorrhizal sorted under a dissection microscope. These mycorrhizas were individually stored in small plastic vials with DNA-conserving solution. Generally, at each site roots from three populations of Arctic willow and roots from two populations of Dryas were collected. In total, about 1200 mycorrhizas from Arctic willow from 14 sites and 400 mycorrhizas from Dryas from 8 sites were collected. The fungal symbionts in these root samples will be discriminated and eventually identified by analysing the fungal DNA. Using specific fungal DNA amplifying oligonucleotides, a part of the fungal nuclear rDNA will be amplified (plant DNA is not amplified) from these mycorrhizas. This DNA fragment will be cut by specific enzymes (restriction enzymes) to generate ”DNA fingerprints”, which subsequently are compared with a database based on sporocarps with known identity. DNA fragment from still unidentified samples will be sequenced and taxonomically grouped by comparison with databases of fungal sequences. During this process, still unknown fungi may be identified. This part of the project is being carried out in collaboration between Anders Dahlberg at the Swedish University of Agricultural Science in Uppsala and Monique Gardes and Jean-Yves Charcosset at the Université Paul Sabatier in Toulouse, France. The molecular analysis, the identification of the fungal symbionts and the exploration of the distribution pattern of Ectomycorrhizal fungi will be conducted in Toulouse during the winter/spring 1999-2000.
Fungal adaptation to cold conditions analysed from 100 kg soil
Arbuscular mycorrhizal fungi do not produce sporocarps at all and roots that are colonised by Arbuscular mycorrhizal fungi need to be stained and observed under microscope to be detected. At all sites in the High Arctic, soil and root samples were collected from plant species that are known from the low Arctic to host Arbuscular mycorrhizal fungi. Potentially and hopefully, Arbuscular mycorrhizal fungi will be present in as many of these samples as possible. In total nearly 100 kg soils was collected in 65 samples from four sites and 20 plants. These samples were stored in a freezer during the expedition and thereafter transported directly to Lund. In order to culture the Arbuscular mycorrhizal fungi, the soil samples have been potted with bait seedlings. If Arbuscular mycorrhizal fungi are present in the soil, they will form mycorrhiza and grow in the roots of the bait seedlings. The physiological properties of the Arbuscular mycorrhizal fungi will then be directly analysed from the mycorrhizal roots. Comparative analyses of the physiological adaptation to low temperature of Arbuscular mycorrhizal fungi from the Arctic and from temperate areas will be analysed by Pål-Axel Olsson and Bengt Söderström at the Lund University.
Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences
Université Paul Sabatier
Université Paul Sabatier
Department of Microbial Ecology, Lund University
Department of Microbial Ecology, Lund University
*Not participating in the expedition