MYCORRHIZAL CHRONOSEQUENCE NEAR EXIT GLACIER, ALASKA

Mycorrhizal fungi associated with plant species may change as vegetati on develops following disturbance. The objectives of this study were t o compare ectomycorrhizae through a chronosequence on deglaciated land from bare mineral soil to mature forest and to determine time require d for mycorrhizal formation on natural seedlings. A chronosequence tha t formed as Exit Glacier retreated enabled us to document changes in m ycorrhizae on existing woody plants, including Populus balsamifera ssp . trichocarpa (Torr. & Gray) Hult. (black cottonwood) that dominates t he early stages, Alnus sinuata (Regel) Rydb. (Sitka alder) that has fe w ectomycorrhizal fungal associates, and Picea sitchensis (Bong.) Carr . (Sitka spruce) that typifies late successional stages. Some seedling s of Populus balsamifera became ectomycorrhizal within 3 weeks of germ ination but most took longer. Although a dark type without clamp conne ctions dominated willows in the second and third stage, it was not a d ominant in the first stage and was rare on Ist year seedlings. Ectomyc orrhizal types differed among successional stages for Populus balsamif era. Diversity increased from early successional stages to later stage s, mostly from an increase in evenness rather than richness. Arbuscula r mycorrhizae were not found on any woody plants, although a few herba ceous plants had low infection percentages.