PARENT SESSION
Oral Session 63: Forest Ecology III: Communities; Diversity; Mycorrhizae.
Presiding: B Kerns and I Ashton
Wednesday, August 4, 8:00 AM to 11:30 AM, Meeting Room C 120.

Thuja plicata exclusion in ectomycorrhiza-dominated forests: Testing the role of inoculum potential of arbuscular mycorrhizal fungi.

Weber, Adrian ¹, Karst, Justine^*,1, Gilbert, Benjamin¹, Kimmins, J¹, ¹ University of British Columbia, Vancouver, British Columbia, Canada

ABSTRACT- The ability of trees dependent on arbuscular mycorrhizal (AM) fungi to establish in ectomycorrhizal forests is unknown. On northern Vancouver Island, Canada, there are sharp boundaries between mixed redcedar (Thuja plicata) – hemlock (Tsuga heterophylla) (CH) stands, and stands of hemlock and amabilis fir (Abies amabilis) (HA). We tested differences in AM colonization of redcedar between ectomycorrhiza-dominated (HA) stands and stands containing redcedar (CH), across a range of light levels. We used a soil bioassay approach to determine whether there was sufficient AM fungal inoculum in the HA tree stands to colonize redcedar seedlings. Seeds of hemlock and redcedar were sown in forest floor samples collected from the two types of forests, and shade treatments ranging from <1% to 53% of full sunlight were imposed. After six months, seedling survival and root and shoot biomass were quantified, and redcedar seedlings were sampled for AM fungal colonization. Hemlock survival and growth did not differ between soil types, suggesting there was no substrate-associated limitation to its establishment in either forest type. Redcedar colonization by AM fungi was significantly correlated with light levels in CH soils but arbuscular mycorrhizas were absent in roots of redcedar seedlings grown in HA soil. Redcedar survival and relative growth rate were significantly greater in the CH than in HA soil; higher growth was due primarily to greater shoot growth in CH soils at high light levels. The low soil inoculum potential for redcedar in ectomycorrhiza-dominated stands may account for the virtual exclusion of redcedar seedlings from these forests.

Key words: ectomycorrhiza, shade, arbuscular mycorrhiza, dispersal