Mycorrhizal chronosequence near Exit Glacier, Alaska

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