Mycorrhizal fungi : unlocking their ecology and role in the establishment and growth performance of different conifer species in nutrient-poor coastal forests

This thesis explored the fungal communities of arbuscular mycorrhizal-dominated Cedar-Hemlock (CH) and ectomycorrhizal-dominated Hemlock-Amabilis fir (HA) forests on northern Vancouver Island, British Columbia, Canada and examined the role of mycorrhizal inoculum potential for conifer seedling productivity. Objectives of this research project were to: (1) examine the mycorrhizal fungal communities and infer the inoculum potential of CH and HA forests, (2) determine whether understory plants in CH and HA forest clearcuts share compatible mycorrhizal fungi with either western redcedar (Thuja plicata) or western hemlock (Tsuga heterophylla), (3) test whether differences in mycorrhizal inoculum potential between forest types influence attributes of seedling performance during reforestation and (4) test effectiveness of providing appropriate mycorrhizal inoculum at the time of planting on conifer seedling performance. Molecular and phylogenetic techniques were utilized to compare mycorrhizal fungal diversity between forest types and to identify mycorrhizal fungal associates of the plant species occurring in clearcuts. In a field trial utilizing seedling bioassays, the role of mycorrhization of western redcedar and western hemlock on seedling growth was evaluated; reciprocal forest floor transfers from uncut forests were incorporated into the project design as inoculation treatments. Though diversity was similar, ectomycorrhizal and saprophytic fungal community composition significantly differed between CH and HA forests; arbuscular mycorrhizae were widespread in CH forests, but rare in HA forests. There was high similarity of arbuscular mycorrhizal fungi to those found in western redcedar among the dominant plant species colonizing CH clearcuts, including the ericoid plant Gaultheria shallon and in Blechnum spicant growing sparsely in HA clearcuts. No alternative ectomycorrhizal host species were detected. Mycorrhization greatly influenced productivity of western redcedar seedlings; without mycorrhizal inoculum, redcedar did not achieve its full growth potential in HA clearcuts. Mycorrhization of western hemlock seedlings did not differ between forest clearcut type or treatment group; however, an inhibitory effect of forest floor collected under mature western redcedar trees on the growth of western hemlock seedlings was unexpectedly detected. These results have implications for sustainable forest management practices, including retention of legacy trees and plants with timber harvesting and inoculation of seedlings with mycorrhizal fungi at the time of planting.Forestry, Faculty ofGraduat