Symbiosis with Frankia sp. benefits the establishment of Alnus viridis ssp. crispa and Alnus incana ssp. rugosa in tailings sand from the Canadian oil sands industry

Canada's oil sands reserves found in an area of about 142,000 km2 in Northern Alberta are estimated to be about 170 billion barrels. Extraction procedures generates oil sands process-affected materials (OSPM), a high pH, high salt and low nutrient residue which contains phytotoxic hydrocarbons. Efficient methods are needed to revegetate impacted landscapes in line with governmental standards. Actinorhizal alders could be used to provide nitrogen in a reclamation program as they are early successional species that naturally colonize harsh habitats and improve the soil conditions. In order to evaluate the extent to which alders can withstand OSPM-generated stress, the growth and development of both green (Alnus viridis (Chaix) DC. ssp. crispa) and speckled (Alnus incana (L.) Moench ssp. rugosa) alders in varying proportions of OSPM mixed with pristine sand (from 0 to 100 %) was assessed both in the presence and the absence of their symbiont, Frankia sp. Alder survival was not impaired by the presence of OSPM, although symbiosis establishment was less efficient when the alders grew in pure OSPM residue. Actinorhizal alders are very tolerant to OSPM: when grown in pure OSPM (100%), their dry biomass was 15 times greater than that of non-nodulated alders. Moreover, symbiotic alders allocated a higher proportion of their biomass to aerial parts, regardless of the OSPM percentage, whereas non-symbiotic alders showed a greater biomass investment in roots. When symbiosis was present, the alders thrived and produced a large amount of biomass that was highly correlated to the total nodule biomass. The pre-inoculation of alder seedlings in commercial greenhouses prior to their outplanting on OSPM-affected reclamation sites could significantly accelerate their growth and development.