Alders are well recognized for their ability to colonize the harsh environments created by either natural processes or human activity. They establish symbiosis with the actinomycete Frankia alni which supplies 70 to 100 % of the plant’s nitrogen requirements. An important challenge facing the oil sands industry in Alberta, Canada, is management of the toxicity of Tailing Sands (TS) that are alkaline, saline and contain Naphthenic Acids (NA).In order to begin to understand how alders, Frankia alni and their symbiosis perform and adapt to these challenging environmental conditions, the tolerance of the microsymbiont (Frankia alni), the host plants (alders) and their symbiosis to speci c compounds found in TS was studied. In addition, the metabolic response of Frankia alni ACN14a to the presence of NA was characterized. The Frankia alni strains tested tolerated both high pH and NA levels in addition to salts near or at the concentrations found in TS. Furthermore, actinorhizal symbiosis can establish itself under these conditions. NaCl was observed to exert the greatest stress on the establishment of symbiosis, decreasing the ef ciency of the actinorhizal symbiosis. Inoculation of the alder plants with Frankia alni induced a signi cant increase in aerial biomass allocation. Finally, intracellular proteins in Frankia alni alni ACN14a whose expression level were in uenced by naphthenic acids were identi ed. Together, these results demonstrate that actinorhizal alders show signi cant promise for use in the revegetation of lands affected by the mine tailings of the Canadian petroleum industry.