Tree Establishment on Post-Mining Waste Soils: Species, Density, and Mixture Effects

Tree establishment to restore degraded boreal post-mining lands is challenged by low soil productivity, a harsh microclimate, and potentially high contaminant levels. The use of mixed vegetation can facilitate the microclimate but increase competition for soil resources. A statistical accounting of plant–plant interactions and adaptation to multispecies conditions is hard to achieve in field experiments; trials under controlled conditions can distinguish effects of planting density and species interactions in the early stages of plant establishment. A greenhouse trial was established in containers (“mesocosms”) with waste rock or fine tailings from gold mines. Pregerminated (1-week-old) seedlings (Alnus viridis subsp. crispa, Picea glauca, Populus tremuloides, Salix arbusculoides) were planted using a Nelder density gradient design, modified for species combinations. A relative competition effect was estimated as a competitiveness index for each species combination, calculated as a ratio of α coefficients in the Holliday growth equation. The specific leaf area (SLA) was measured to indicate plant water stress adaptation. All species grew better in monoculture on fine tailings, while only P. tremuloides grew better in all mixtures on waste rock. Although net positive effects of density on SLA increment during early growth suggested microclimate improvement on fine tailings, no mixture provided advantages for both species in paired combinations

Mycorrhizae and Rhizobacteria on Precambrian Rocky Gold Mine Tailings: II. Mine-Adapted Symbionts Alleviate Soil Element Imbalance for a Better Nutritional Status of White Spruce Seedlings

In the context of a phytorestoration project, the purpose of this study was to assess the respective contribution to the nutritional status of Picea glauca seedlings of ectomycorrhizae and rhizobacteria native or not to the Sigma-Lamaque gold mine wastes in northern Quebec, Canada. In a glasshouse experiment, inoculated plants were grown for 32 weeks on coarse waste rocks or fine tailings obtained from the mining site. The survival, health, growth, and nutritional status of plants were better on coarse waste rocks than on fine tailings. Fe and Ca were especially found at high levels in plant tissues but at much lower concentrations on waste rocks. Interestingly, inoculation of microsymbionts had only minimal effects on N, P, K, and Mg plant status that were indeed close or within the concentration range encountered in healthy seedlings. However, both fungal and bacterial treatments improved Fe and Ca concentrations in plant tissues. Fe concentration in the foliage of plants inoculated with the fungi Tricholoma scalpturatum Tri. scalp. MBN0213 GenBank #KC840613 and Cadophora finlandia Cad. fin. MBN0213 GenBank #KC840625 was reduced by >50%. Both fungi were isolated from the mining site. The rhizobacteria, Azotobacter chroococcum, also improved plant Fe level in some cases. Regarding Ca nutritional status, the native bacterial strain Pseudomonas putida MBN0213 GenBank #AY391278 was the only symbiont that reduced foliar content by up to 23%. Ca concentration was negatively correlated with the fungal mycorrhization rate of seedling roots. This relation was especially strong (r = -0.66, p-value ≤ 0.0001) in the case of C. finlandia. Also, a similar relationship existed with root Fe concentration (r = -0.44, p-value ≤ 0.0001). In fact, results showed that seedling performance was more correlated with elevated Ca and Fe concentration in planta than with nutrient deficiency. Also, native microsymbionts were capable of regulating seedling nutrition in the poor substrate of the Sigma-Lamaque gold mine tailings

Relationship between plant growth and organic acid exudates from ectomycorrhizal and non-ectomycorrhizal Pinus patula

Plant–mycorrhizal interaction is an important association in the ecosystem with significant impacts on the physical, biological and chemical properties of the soil. In the present study, potential relationships that exist between organic acid production by ectomycorrhizal pine seedlings and plant parameters in the absence of any significant environmental stress were investigated. The aim of the study was to investigate the contribution of organic acid production to plant growth. Four different ectomycorrhizal fungi were used in a mycorrhizal synthesis experiment to colonise roots of Pinus patula. Ectomycorrhizal and nonectomycorrhizal plants were used in a pot trial experiment that lasted for 24 weeks. After harvesting, plant materials as well as soil samples underwent different analyses, which included the determination of pH, organic acids, plant biomass, and foliar and root phosphorus and potassium. The results indicated a significant interaction (P < 0.0001) between fungal type and organic acid production. This reflects the influence of fungal type on organic acid production. However, it was observed that organic acids secreted into the soil do not have a direct link to the quantity of nutrients detected in either the root or shoot, but seemed to positively influence plant growth as reflected in the result from root and shoot biomass.http://www.tandfonline.com/loi/tjps202016-06-04hb201

Edaphic Selection Pressures as Drivers of Contrasting White Spruce Ectomycorrhizal Fungal Community Structure and Diversity in the Canadian Boreal Forest of Abitibi-Témiscamingue Region.

Little is known about edaphic selection pressures as drivers of contrasting white spruce ectomycorrhizal fungal community structure and diversity in the Canadian boreal forest. We hypothesized that community composition differs among the four sites sampled-nursery, mining site, forest edge, and natural forest. Ectomycorrhizal (ECM) fungal community structure and diversity was studied at the four locations with soil fertility gradient through morpho-molecular and phylogenetic analyses in relationships with rhizospheric soil chemical properties. 41 different species were identified. Mining site had a significantly different species composition than the surrounding environments. Soil pH and percentage of roots colonized by ECM fungi increased while soil P, N, Fe, C, K, Mg, Al, Ca, and Na contents declined across the soil fertility gradient: nursery → natural forest → forest edge → mining site. Contrary to the preference of acid soils by ECM fungi, a few ecologically adapted to high pH, poor soil chemical fertility, and low organic matter content colonize white spruce roots on the non-acidogenic mining site, allowing natural regeneration of white spruce seedlings. Other ECM fungi are adapted to high fertigation level of commercial nursery. This study clearly shows the contrasting difference in white spruce ectomycorrhizal fungal community structure and diversity driven by edaphic selection pressures

Genetic Diversity and Population Structure of a Threatened African Tree Species, Milicia excelsa, Using Nuclear Microsatellites DNA Markers

To accurately estimate the genetic diversity and population structure for improved conservation planning of Milicia excelsa tree, 212 individuals from twelve population samples covering the species' range in Benin were surveyed at seven specific microsatellite DNA loci. All loci were variable, with the mean number of alleles per locus ranging from 5.86 to 7.69. Considerable genetic variability was detected for all populations at the seven loci (AR=4.60; HE=0.811). Moderate but statistically significant genetic differentiation was found among populations considering both FST (0.112) and RST (0.342). All of the populations showed heterozygosity deficits in test of Hardy-Weinberg Equilibrium and significantly positive FIS values due to inbreeding occurring in the species. Pairwise FST values were positively and significantly correlated with geographical distances (r=0.432; P=.007, Mantel's test) indicating that populations are differentiated by “isolation by distance.” Bayesian analysis of population structure showed division of the genetic variation into four clusters revealing the existence of heterogeneity in population genetic structure. Altogether, these results indicate that genetic variation in Milicia excelsa is geographically structured. Information gained from this study also emphasized the need for in situ conservation of the relict populations and establishment of gene flow corridors through agroforestry systems for interconnecting these remnant populations

Mycorrhizae and Rhizobacteria on Precambrian Rocky Gold Mine Tailings: I. Mine-Adapted Symbionts Promote White Spruce Health and Growth

White spruce [Picea glauca (Moench) Voss] is a commercially valuable boreal tree that has been known for its ability to colonize deglaciated rock tailings. Over the last decade, there has been an increasing interest in using this species for the revegetation and successful restoration of abandoned mine spoils. Herein, we conducted a glasshouse experiment to screen mycorrhizal fungi and rhizobacteria capable of improving the health and growth of white spruce seedlings growing directly on waste rocks (WRs) or fine tailings (FTs) from the Sigma-Lamaque gold mine located in the Canadian Abitibi region. After 32 weeks, measurements of health, growth, and mycorrhizal colonization variables of seedlings were performed. Overall, symbionts isolated from roots of healthy white spruce seedlings growing on the mining site, especially Cadophora finlandia Cad. fin. MBN0213 GenBank No. KC840625 and Pseudomonas putida MBN0213 GenBank No. AY391278, were more efficient in enhancing seedling health and growth than allochthonous species and constitute promising microbial symbionts. In general, mycorrhizae promoted plant health and belowground development, while rhizobacteria enhanced aboveground plant biomass. The observed beneficial effects were substrate-, strain-, and/or strains combination-specific. Therefore, preliminary experiments in control conditions such as the one described here can be part of an efficient and integrated strategy to select ecologically well-adapted symbiotic microorganisms, critical for the success of a long-term revegetation program

Two-way cluster analysis (α = 0.05) showing groups of species thriving in same habitats (small coloured rectangles) (darker grey squares mean higher abundance; Big red rectangle = no difference between site species composition).

<p>Two-way cluster analysis (α = 0.05) showing groups of species thriving in same habitats (small coloured rectangles) (darker grey squares mean higher abundance; Big red rectangle = no difference between site species composition).</p

Principal component analysis (α = 0.05) showing linear patterns of a wide range of variables across the ecological gradient (Sampling sites: MS = mining site, FE = forest edge, NF = naturel forest, and TN = Trecesson nursery) (only the axis 1 is significant; closer to center means smaller values) (MYC = % of roots colonized by ECM fungi).

<p>Principal component analysis (α = 0.05) showing linear patterns of a wide range of variables across the ecological gradient (Sampling sites: MS = mining site, FE = forest edge, NF = naturel forest, and TN = Trecesson nursery) (only the axis 1 is significant; closer to center means smaller values) (MYC = % of roots colonized by ECM fungi).</p

Combining alders, frankiae, and mycorrhizae for the revegetation and remediation of contaminated ecosystems

Alder shrubs and trees that are capable of forming symbioses with mycorrhizal fungi and the nitrogen-fixing actinomycete Frankia sp. are particularly hardy species found worldwide in harsh and nutrient-deficient ecosystems. The mycorrhizal symbiosis may assist alders in nutrient and water uptake, while the actinorhizal symbiosis provides assimilable nitrogen. It is through these highly efficient symbioses, in which microsymbionts benefit from plant photosynthates, that actinorhizal plants such as alders colonize poor substrates, enrich soil, and initiate plant succession. These natural capabilities, combined with careful screening of microsymbionts and host plants, may prove useful for the rehabilitation of disturbed ecosystems. Although alders have been used extensively at industrial scales in forestry, nurse planting, and contaminated land revegetation, relatively little research has focussed on their actinorhizal and mycorrhizal plant-microbe interactions in contaminated environments. To study such a topic is, however, critical to the successful development of phytotechnologies, and to understand the impact of anthropogenic stress on these organisms. In this review, we discuss two alder-based phytotechnologies that hold promise: the stimulation of organic contaminant biodegradation (rhizodegradation) by soil microflora in the presence of alders, and the phytostabilization of inorganic contaminants. We also summarize the plant-microbe interactions that characterize alders, and discuss important issues related to the study of actinorhizal and (or) mycorrhizal alders for the rehabilitation of disturbed soils.Les aulnes arbustifs et arborescents, formant des symbioses avec des champignons mycorhiziens et les actinomyc\ue8tes fixateurs Frankia sp., sont des esp\ue8ces particuli\ue8rement robustes qu'on retrouve partout au monde, dans des \ue9co-syst\ue8mes inhospitaliers et pauvres en nutriments. La symbiose mycorhizienne peut assister les aulnes dans l'absorption de l'eau et des nutriments, alors que la symbiose actinorhizienne fournit l'azote assimilable. c'est par l'interm\ue9diaire de ces symbioses tr\ue8s efficaces, o\uf9 les microsymbiontes obtiennent les photosynth\ue9tats de la plante, que les plantes actinorhiziennes, telles que les aulnes, colonisent des substrats pauvres, enrichissent le sol et initient la succession v\ue9g\ue9tale. Ces capacit\ue9s naturelles combin\ue9es avec une s\ue9lection soign\ue9e des microsymbiontes et des plantes h\uf4tes, peuvent s'av\ue9rer utiles pour la r\ue9habilitation d'\ue9cosyst\ue8mes perturb\ue9s. Bien qu'on ait largement utilis\ue9 les aulnes \ue0 l'\ue9chelle industrielle en foresterie, comme plantes compagnes et pour la r\ue9habilitation des sols contamin\ue9s, relativement peu de recherches ont port\ue9 sur leurs interactions actinorhiziennes et mycorhiziennes plante-microbe, dans des environnements contamin\ue9s. Cependant, l'\ue9tude de ce sujet est n\ue9cessaire pour d\ue9velopper des phytotechnologies efficaces et pour comprendre l'impact des stress anthropog\ue8nes sur ces organismes. Dans cette revue, les auteurs discutent dux phytotechnologies prometteuses bas\ue9es sur l'aulne; la stimulation de la biod\ue9gradation (rhizod\ue9gradation) par la microflore du sol en pr\ue9sence d'aulnes, et la phytostabilisation, des contaminants organiques. Les auteurs r\ue9sument \ue9galement les interactions plante-microbe qui caract\ue9risent les aulnes et discutent de questions pertinentes reli\ue9es \ue0 l'\ue9tude des aulnes actinorhiziens et (ou) mycorhiziens, pour la r\ue9habilitation des sols perturb\ue9s.NRC publication: Ye