Mycorrhizal symbiosis plays a key role in ecological processes like plant succession through the redistribution of resources among host plants with different needs. Primary succession of vegetation in post-mining areas offers great opportunities to study how mycorrhizal symbiosis influences the revegetation of degraded environments. In this study, we aim to determine how seedling growth is affected by below-ground facilitation via mycorrhizal networks. Specifically, we determine 1) existing mycorrhizal communities, 2) the effect of variables such as host identity and spatial structure on mycorrhizal sharing among hosts and 3) how these mycorrhizal communities, along with other defined physical and biological factors, affect tree growth in a harsh environment. The study site is the mine tailings site of the Beattie Gold Mine near Lake Duparquet in north-western Quebec and two 15 x 15 m plots were inventoried at this site. Betula papyrifera, Populus balsamifera, Picea glauca and Thuja occidentalis were used as focal species and the effect of neighbouring plants was identified. Communities of mycorrhizal fungi were sequenced using molecular markers and analyzed to detect possible species sharing. We identified 474 fungal operational taxonomic units (OTUs) from the fungal DNA amplified samples. Among the 474 OTUs, 52 ectomycorrhizal OTUs and 20 arbuscular mycorrhizal OTUs were identified. Host specificity was not detected as ectomycorrhizal species were shared among all host species and priority effects drove the mycorrhizal community structure of host plant individuals rather than host specificity.

Mycorrhizal composition did not vary between plots nor spatially within each plot. Soil nitrogen and phosphorus concentration were extremely low and high arsenic levels were detected in the field. Neighborhood competition indices, soil nitrogen, shoot biomass, mycorrhizal richness, mycorrhizal abundance and sharing of mycorrhizae among host plants did not affect the growth of most host plants. This study concludes that plant-plant interactions (competition or facilitation), mycorrhizal networks and local variations in the concentration of soil nutrients are not important factors for determination of plant growth and vegetalization at our study site due to the harsh environmental conditions. This study helps to develop appropriate strategies for reforestation of boreal forests in mining sites.