Ectomycorrhizal fungi of whitebark pine (Pinus albicaulis) in the Northern Greater Yellowstone Ecosystem
Mohatt, Katherine Rose
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Whitebark pine (Pinus albicaulis) is an integral component of subalpine ecosystems in the Western United States where it is considered a keystone species. The mature forests which colonize harsh treeline terrain provide habitat for flora and fauna an essential food source to grizzly bears, and are also important in watershed dynamics. Threats which have led to the decline of this tree species, up to 40-90% in parts of its range, include blister rust, mountain pine beetle, fire suppression, and climate change. Pines are obligate ectomycorrhizal symbionts, and host mutualistic fungi on their roots beneficial to tree establishment and sustainability; however, little is known of the ectomycorrhizal (ECM) fungi crucial to the survival of P. albicaulis. The goal of this study was to discover the species of ECM fungi associated with P. albicaulis in the Northern Greater Yellowstone Ecosystem. A survey of fruiting structures of ECM fungi in mature P. albicaulis forests from five mountain ranges revealed at least 44 species. ECM fungi in the Boletales and Cortinariales comprised 50% of the species, 24% were hypogeous, and one Chroogomphus species is new to science. An examination of the roots of P. albicaulis seedlings using morphotyping and sequencing of the ITS region revealed 19 species of ECM fungi, 11 of which were not previously revealed by sporocarps, including 2 Tomentelloid types. Cenococcum geophilum was the most frequent (64% of seedlings) and abundant (49% of root tips) ECM fungus on roots. Pinus albicaulis seeds are primarily distributed by Clark's nutcrackers which cache seed on open slopes at a distance from mature forests. A comparison of the ECM fungi on seedlings in avalanche paths and adjacent mature forests on Scotch Bonnet Mountain revealed a similar species richness, however species composition only partially overlapped . Of necessity, some "seedling clusters" were sampled instead of single seedlings, mostly from paths and they appeared to host more ECM fungi, which likely skewed results. Current efforts to restore this tree, especially by the out-planting of rust-resistant seedlings, can benefit from this research as a knowledge of the ECM fungi could help reestablish this tree in peril.