Performance of ectomycorrhizal alders exposed to specific Canadian oil sands tailing stressors under in vivo bipartite symbiotic conditions.

Canadian oil sands tailings are predominately sodic residues contaminated by hydrocarbons such as naphthenic acids. These conditions are harsh for plant development. In this study, we evaluated the effect of inoculating roots of Alnus viridis ssp. crispa and Alnus incana ssp. rugosa with ectomycorrhizal fungi in the presence of tailings compounds. Seedlings were inoculated with 7 different strains of Paxillus involutus and Alpova diplophloeus and were grown under different treatments of NaCl, Na2SO4, and naphthenic acids in a growth chamber. Afterwards, seedling survival, height, dry biomass, leaf necrosis, and root mycorrhization rate were measured. Paxillus involutus Mai was the most successful strain in enhancing alder survival, health, and growth. Seedlings inoculated with this strain displayed a 25% increase in survival rate, 2-fold greater biomass, and 2-fold less leaf necrosis compared with controls. Contrary to our expectations, A. diplophloeus was not as effective as P. involutus in improving seedling fitness, likely because it did not form ectomycorrhizae on roots of either alder species. High intraspecific variation characterized strains of P. involutus in their ability to stimulate alder height and growth and to minimize leaf necrosis. We conclude that in vivo selection under bipartite symbiotic conditions is essential to select effective strains that will be of use for the revegetation and reclamation of derelict lands.

In vitro selection of ecologically adapted ectomycorrhizal fungi through production of fungal biomass and metabolites for use in reclamation of biotite mine tailings.

Mineral weathering plays an important role in poor-nutrient environments such as mine spoils and tailings. Ectomycorrhizal (ECM) fungi are able to enhance mineral weathering through different mechanisms, thereby increasing the availability of minerals and nutrients to plants. Six ECM fungi (Cadophora finlandia, Cenococcum geophilum, Hebeloma crustuliniforme, Lactarius aurantiosordidus, Paxillus involutes, and Tricholoma scalpturatum) were tested here for their tolerance to biotite-quartz-rich mine tailings. Either solid- or liquid-medium methods were used for in vitro selection of ECM fungi for their ability to grow on mine tailings. ECM fungi were selected based on their mycelial radial growth and metabolite production (ergosterol and low-molecular-mass organic acids, LMMOAs). We found a strong correlation between fungal ergosterol content and mycelial radial growth using the solid-medium method. However, the liquid-medium method was more appropriate for ergosterol synthesis and permitted direct measurement of organic acid production. We found that LMMOAs were exuded by ECM fungi, which solubilized mine tailings for their own growth and nutrition. Finally, we concluded that the ECM fungi C. finlandia and T. scalpturatum are the species most tolerant to tailings and could potentially improve the survival rate, growth, and health of white spruce seedlings planted on biotite mine spoils and tailings.