ECTOMYCORRHIZAE, ARBUSCULAR MYCORRHIZAE, AND RHIZOCTONIA SP OF ALPINE AND BOREAL SALIX SPP IN NORWAY

The extent of occurrence of mycorrhiza in genus Salix and relationships among root symbionts of nine Salix species from middle boreal forest to alpine zones in Norway were examined. A common nonmycorrhizal endophyte documented was Rhizoctonia sp. All plant species were found associated with calcareous soils and shallow fens and were colonized by ectomycorrhizal (ECM) or arbuscular mycorrhizal (AM) fungi and Rhizoctonia sp. Rhizoctonia sp. did not show any discernible patterns in relation to colonization of roots by mycorrhizal fungi. Three obvious types of AM and ECM fungal distributions within/on the roots were recognized, occurring either singly or dually. In dual mycorrhizal conditions, Hebaloma sp., an ECM fungus, was consistently found associated with AM fungal colonization: this combination occurred in only two Salix species. The occurrence of ECM fungal colonization of Salix spp. roots was negatively associated with the occurrence of AM fungi and Rhizoctonia sp. colonization. In contrast, AM fungal colonization was positively associated with that of Rhizoctonia sp. Although not conclusive, the data support earlier observations that AM fungi are likely replaced by ECM fungi.