Mycorrhizas and dark septate root endophytes in polar regions
We review the distributions and functions of mycorrhizas and dark septate root endophytes in polar regions. Arbuscular mycorrhizas (AM) are present in the Arctic and Antarctic to 82 ºN and 63 ºS, respectively, with fine endophyte being the dominant form of AM in roots at higher latitudes. Ecto- (ECM) and ericoid (ERM) mycorrhizas both occur in the Arctic to 79 ºN, owing to the presence of species of Salix, Dryas, Vaccinium and Cassiope to this latitude. ECM and ERM are not present in Antarctic ecosystems, owing to an absence of suitable hosts. Arbutoid and orchid mycorrhizas are infrequent in the Arctic, whilst the latter is present at one location in the sub-Antarctic. Data from studies of AM, ECM and ERM colonisation along a latitudinal transect through the Arctic indicate that the frequency of plant species not colonised by mycorrhizas increases at higher latitudes, largely owing to an increase in non-mycorrhizal and a decrease in obligately mycorrhizal plant families at more northerly locations. A separate group of root- and rhizoid-associated fungi, the dark septate root endophytes (DSE), are widespread to 82 ºN and 77 ºS, and are apparently more frequent than mycorrhizal fungi in polar regions. The functions of DSE are largely unclear, but studies suggest beneficial effects on plant growth under defined conditions. We advocate further research into the effects of DSE on their host plants in polar regions.