Fugitive mine dust (i.e., particulate emissions) is a ubiquitous waste stream at all mine sites, including active, inactive, and abandoned. Although dust emissions can reasonably be expected to diminish after the cessation of mining activities, any waste products left uncovered have the potential to continue to emit dust to the near-mine environment. In this study, we capture and characterize dust using the Pas-DD dustfall method around the inactive gold-mine site of Joutel in the Abitibi-Témiscamingue region of Québec. The site has been inactive for 30 years, during which time the tailings storage area has been left mostly uncovered, with previously unknown amounts of dust entering the near-mine environment. The quantity of dust captured by our samplers was generally low and did not exceed 0.5 mg/dm2day. Areas of the bottom ∼2 mm of the polyurethane foam (PUF) disks used as a sampling substrate in the Pas-DD method partially degraded following deployment for 284–285 days in the field, resulting in a mass loss of up to 0.57 mg/dm2day. The low dust deposition rates and variable amounts of PUF degradation precluded net mass flux of the PUF disks providing meaningful insight into spatial variability of dust deposition. In contrast, element deposition rates and quantitative mineralogy of the dust are not impacted by PUF degradation and were the most useful datasets in this low-dust setting, allowing us to distinguish background environmental dust from local anthropogenic dust sources, including the tailings as well as other activities in the area. The major (average > 5 vol%) minerals in the dust are: muscovite (21 ± 6 vol%), quartz (22 ± 16 vol%), feldspars (18 ± 4 vol%), chlorite (13 ± 3 vol%), and olivine or serpentine (5 ± 3 vol%). All of these minerals except olivine or serpentine were also common in the tailings, in similar abundance except for reduced muscovite (3.9 ± 0.6 vol% muscovite, 27 ± 7 vol% quartz, 19 ± 3 vol% feldspars, 10 ± 5 vol% chlorite). The tailings also had iron (hydr)oxides (21 ± 8 vol%) and sometimes pyrite (14 ± 19 vol%) as major minerals. The minerals that were identified as being derived mainly from the tailings site are iron (hydr)oxides, ankerite, and pyrite whereas olivine or serpentine, amphibole, calcite, and dolomite originate primarily from the background Abitibi Greenstone Belt environment. Dust with the highest proportion of tailings-sourced minerals was captured downwind of the site and decreased in abundance with distance, pointing to wind as the primary control on dust dispersion from the tailings, with other activity in the forest near the site or along the roads producing discreet dust-generating events. The captured dust contained distinctly less Fe and As than the tailings, reflecting the much lower proportion of iron (hydr)oxides and pyrite in the dust compared to the tailings. Differences in the relative proportion of minerals in the dust compared to the tailings reflect the preferential mobilization of minerals with lower density and flaky mineral habits. Overall, this study demonstrates the utility of the Pas-DD dust monitoring method in a low-dust setting and the central role that the physical properties of minerals play in the resulting dust composition.

The soil microbiome plays a key role in tree growth and nutrient cycling. Although hybrid poplar clones are phylogenetically related, their influence on the soil microbiome may differ due to phenotypic differences, especially their root mean diameter or mass density (RMD). This influence remains relatively unexplored, limiting our understanding of how soil microbial communities contribute to the growth strategies of fast-growing trees. Our objective was to determine how phylogenetically related trees and their root traits influence soil microbial diversity and composition by studying five hybrid poplar clones growing in a plantation located in New Liskeard, Ontario, Canada. We collected soil cores at depths of 0–20 cm (topsoil) and 20–40 cm (subsoil) and analyzed fine root traits and soil bacterial and fungal communities. We found that phylogenetically related hybrid poplars influenced the soil microbiome by shaping the composition of microbial communities. Differences between clones were evident in the relative abundance of soil ectomycorrhizal fungi and Actinobacteriota in both topsoil and subsoil. The increase in relative abundance of ectomycorrhizal fungi was driven by high RMD and root length density (RLD), i.e., high fine root mass and length per unit soil volume. Fine roots with high RLD led to a higher relative abundance of Actinobacteriota in the topsoil, while recalcitrant fine roots (high lignin/nitrogen ratio) promoted their abundance in the subsoil. Thus, root traits are key factors in determining the effects of trees on soil microbiome. The soil microbiome, together with root traits, could be an important aspect to consider in tree selection.

On pourrait dire que la forêt boréale est comme un grand orchestre, où chaque instrument joue son rôle pour produire une harmonie. Les mousses, en particulier, sont comme les musiciennes de fond, souvent discrètes, mais essentielles à l’équilibre de l’ensemble. Si vous marchez en forêt, vous les verrez couvrir le sol comme un doux tapis vert. À la manière de l’isolant dans une maison, elles gardent le sol frais, humide et régulent la température. Les mousses abritent diverses bactéries qui aident à nourrir la forêt, tels des chefs d’orchestre invisibles qui donnent la tonalité à l’ensemble du système. Cette association représente jusqu’à 50 % des apports en azote dans la forêt boréale.

In recent years, plant–microorganism interactions and their impact on plant growth and health, and in turn on plant-driven ecosystem services (e.g., carbon storage, phytoremediation) have gained a lot of interest in the scientific community. This interest has been stimulated by the development of high-throughput sequencing technologies that greatly improved the capacity of scientists to efficiently characterize microbiomes, which are defined as the pool of genomes of the microorganisms (e.g., bacteria, fungi) present in a particular habitat. Among trees, the poplar microbiome is one of the most extensively studied. The goal of this chapter is to summarize the current literature on the poplar microbiome, first by describing the microbiomes of belowground and aboveground parts of poplars, and second by highlighting links between poplar genetic and the microbiome. This second part includes a review of studies specifically addressing the impact of transgenesis on the poplar microbiome. Overall, this chapter highlights the diversity of the poplar microbiome and the importance of further assessing links between tree genetic and the microbiome.

In eastern Canada, boreal forests are locally experiencing a shift between two alternative stable states, productive closed-canopy feather moss (Pleurozium schreberi (Brid.) Mitt.) forests to low-productivity open lichen (Cladonia spp.) woodlands. While this shift has important consequences for ecosystem structure and productivity, little is known about the changes occurring in the diversity and composition of the soil microbial community which may be driven by this process. We evaluated the effects of 10-year moss transplantation on soil microbial communities in an open-lichen woodland. Treatments included: 1) removal of the lichen cover, 2) removal of the lichen cover followed by transplantation of a feather moss cover, 3) a control with the lichen cover kept in place (lichen control), and 4) a natural forest site with a feather moss cover (moss control). We found that changing the forest ground cover has a significant impact on the diversity, composition and function of soil microbial communities. Fungal alpha diversity was more sensitive to changes in lichen and moss cover, compared to bacterial diversity. Soil microbial community composition showed significant differences among all forest ground covers, but with greater similarities between the moss transplantation and control moss treatments. More importantly, changes of forest ground cover significantly affected the structure of microbial communities and fungal functional groups. Moss transplantation significantly increased the relative abundance of the organic nitrogen-scavenging fungal genus, Piloderma. Furthermore, moss transplantation significantly increased the overall relative abundance of ectomycorrhizal fungi and decreased the proportion of ericoid mycorrhizal fungi. Soil moisture and temperature were the main environmental variables associated to the shift in microbial community composition. Our study points out that moss transplantation in open-canopy lichen woodlands contributes to regulate and modify the composition, structure, and function of the soil microbial communities with potential implications for explaining the changes in ecosystem processes associated with these two forest ecosystems.

Global change is shifting ecosystem type relative abundance in boreal forests, while the green energy transition results in increased mining activities around the globe. The interaction and consequent effects of these two trends on biodiversity have not been examined in depth. Bryophytes species can be used as indicators to measure these effects because they play key ecological roles in boreal forests. We identified and evaluated the interaction between ecosystem type (i.e., coniferous, deciduous, mixed forest and open canopy) and mining on microhabitat scale bryophyte diversity and composition in 1-km landscapes surrounding six mine sites at different stages of the mining lifecycle in the Canadian boreal forest. Irrespective of microhabitat type, the combined effects of ecosystem type and mining stage were interactive on bryophytes. Bryophyte richness and community composition were negatively affected by offsite effects of mines in only deciduous and mixed forests. The interacted effects on bryophyte richness mainly occurred on the ground r microhabitats. We also found that deciduous, mixed forests (coniferous forest as a reference) and mines had a negative impact on the abundance of feather mosses and sphagna. Furthermore, indicator species were identified for areas affected by mines (Pohlia nutans and Dicranum polysetum) and for control areas (Sphagnum angustifolium and Plagiomnium cuspidatum). Our results suggest the predicted ecosystem shifts with global changes, from coniferous to deciduous forests, could potentially increase the effects of mining on forest ecosystem resistance through the changes in bryophyte community structure. Adding microhabitats (i.e., adding coarse woody debris) near mine sites is a potential strategy to maintain species richness. Collectively, these findings advance our understanding of how mining affects biodiversity and highlight the importance of considering mine offsite landscapes in future environmental evaluations of development projects in the context of global changes.