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We tested the effects of ectomycorrhizal (ECM) inoculation on greenhouse-grown white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana L.) seedlings to be used for revegetation of salt-affected tailing sands resulting from the exploitation of oil sand in northeastern Alberta, Canada. White spruce and jack pine seedlings were inoculated with three ECM fungi selected for their in vitro tolerance to excess Na+ and Cl-: Hebeloma crustuliniforme (Bull) Quel. UAMH 5247, Laccaria bicolor Maire (Orton) UAMH 8232 and a Suillus tomentosus (Kauff.) Sing., Snell and Dick isolate from a salt-affected site. The physiological responses of the seedlings to a gradient of NaCl concentration (0, 50, 100 and 200 mM) were assessed over four weeks by: (1) Na+ accumulation and allocation; (2) chlorophyll a fluorescence; (3) growth, (4) water content; and (5) organic osmolyte accumulation. Jack pine seedlings were more sensitive than white spruce seedlings to increasing Na+ and Cl- concentrations. Both species showed decreasing biomass accumulation, and increasing concentrations of organic osmotica and Na with increasing NaCl concentration. White spruce seedlings inoculated with the S. tomentosus isolate had the best growth response at all NaCl concentrations tested. Although jack pine seedlings inoculated with the L. bicolor or S. tomentosus isolate exhibited the highest growth in the 50 and 100 mM NaCl treatments, both fungi increased the photochemical stress and dehydration of their hosts in the 200 mM NaCl treatment. At the latter concentration, jack pine seedlings inoculated with H. crustuliniforme showed the greatest tolerance to salt stress. Although the different fungi altered the physiological response of the host in different ways, inoculation with salt-stress-tolerant ECM fungi increased growth and reduced the negative effects of excess NaCl. Use of controlled mycorrhization may increase survival of coniferous seedlings used for revegetation of salt-affected sites.

The oil sand industry in northeastern Alberta produces vast areas of severely disturbed land. The sodicity of these anthropic soils is one of the principal constraints that impede their revegetation. Previous in vitro studies have shown that the ectomycorrhizal fungi Laccaria bicolor (Maire) Orton UAMH 8232 and Hebeloma crustuliniforme (Bull) Quel. UAMH 5247 have certain salt-resistant traits and thus are candidate species for the inoculation of tree seedlings to be outplanted on salt-affected soil. In this study, the in vitro development of these fungi was compared to that of three mycorrhizal fungi [Suillus tomentosus (Kauff.) Sing., Snell and Dick; Hymenoscyphus sp. and Phialocephala sp.] isolated from a sodic site created by Syncrude Canada Ltd. Their growth, osmotica and Na/Cl contents were assessed over a range (0, 50, 100, 200 mM) of NaCl concentrations. After 21 days, the two ascomycetes (Hymenoscyphus sp. and Phialocephala sp.) were shown to be more resistant to the NaCl treatments than the three basidiomycete species. Of the basidiomycetes, L. bicolor was the most sensitive to NaCl stress, while H. crustuliniforme showed greater water stress resistance, and the S. tomentosus isolate exhibited greater Na and Cl filtering capacities and had a better biomass yield over the NaCl gradient tested. Both ascomycetes used mechanisms other than carbohydrate accumulation to palliate NaCl stress. While the Hymenoscyphus isolate accumulated proline in response to NaCl treatments, the darker Phialocephala isolate may have used compounds such as melanin. The basidiomycete species accumulated mainly mannitol and/or proline in response to increasing concentrations of NaCl.

In order to select woody plant candidates suitable for revegetation of saline-alkaline soils, we tested selected woody plant species and seed lots: Pinus contorta (lodgepole pine), Pinus banksiana (jack pine), Picea glauca (white spruce), Populus tremuloides (trembling aspen), and Alnus rubra, syn. Alnus oregona (red alder). Pre-germinated seedlings were grown for 4 weeks in a greenhouse in a semi-hydroponic system containing 1/2 strength Hoagland solution with additional sodium concentrations (0, 25, 50, 75 mM) and composite tailings release water. A significant interaction between salt treatments and seed lots within plant species as well as between salt treatments and plant species was observed for weight and necrosis, indicating that the plant genotype responded differently to salt treatments. Of all examined woody plant species, jack pine (Syncrude seed source) exhibited the highest percent survival followed by white spruce (Syncrude seed source), red alder (seed lot No. 40457), and lodgepole pine (seed lot No. 7960007). Proportionately ranked means for dry biomass production showed lodgepole pine (seed lot No. 7960007) with the greatest biomass followed by aspen (seed lot No. Syncrude), red alder (seed lot No. Port Renfrew), jack pine (seed lot No. 8960049) and white spruce (Syncrude seed source). The best performing seed lots based on aggregation index which combines both the percent survival and dry weight averages were: red alder (seed lot Nos. 40457 and 45958), aspen (Syncrude seed source), jack pine (Syncrude seed source), lodgepole pine (seed lot No. 7960007). Based on variance components, most of the variation was explained by the treatment and seed lot effects. This reveals the importance of intra-specific variability and that selection should be based not only on inter-specific variation but also on the intra-specific variation for the development of salt-tolerant lines to be used in reclamation of saline habitats. #