Edaphic factors determining the colonization of semiarid mine tailings by a ruderal shrub and two tree plant species: Implications for phytomanagement

Evaluation of the rhizospheric microbiome of the native colonizer Piptatherum miliaceum in semiarid mine tailings

The study of the rhizospheric microbiome in native plants should be a prerequisite before carrying out the phytomanagement of mine tailings. The goal of this work was to evaluate the rhizospheric microbiome of Piptatherum miliaceum in semiarid mine tailings. A comprehensive edaphic characterization was performed including the description of soil microbial composition in the rhizosphere of P. miliaceum growing at a mine tailings pile and at a control site. Plant nutritional and isotopic compositions were also determined. Neutral pH of the tailings (7.3) determined low metal extractability in 0.01 M CaCl2 (e.g. < 1 mg/kg for Zn). In spite of the contrasting edaphic fertility conditions of both sites, N (~ 15 g kg-1) and P (~ 400 mg kg-1) leaf concentrations were similar. The lower δ15N at the tailings plants (- 4.50‰) compared to the control (6.42‰) indicated greater efficiency of P. miliaceum for uptaking N under the low fertility conditions of the tailings (0.1% total soil nitrogen). The presence at the tailings of bacterial orders related to the cycling of N, such as Rhizobiales, could have contributed to enhance N acquisition. The lower leaf δ13C values at the tailings (- 30.22‰) compared to the control (- 28.47‰) indicated lower water use efficiency of the tailing plants. Some organotrophic bacterial and fungal groups in the tailings' rhizospheres were also found in the control site (e.g. Cytophagales, Sphingobacteriales for bacteria; Hypocreales, Pleosporales for fungi). This may indicate that P. miliaceum is able to shape its own specific microbiome at the tailings independently from the initial microbial composition of the tailings.

Synergistic enhancement of the phytostabilization of a semiarid mine tailing by a combination of organic amendment and native microorganisms (Funneliformis mosseae and Bacillus cereus)

The goal of this work was to evaluate the effects of fermented sugar beet residue and inoculation with a native arbuscular mycorrhizal (AM) fungus, Funneliformis mosseae (Nicol. and Gerd.) Gerd. and Trappe, or a native bacterium, Bacillus cereus Frankland & Frankland, alone or in combination, on the establishment of Lygeum spartum L. seedlings grown in a mine tailing under semiarid conditions. We conducted a field study to analyse root and shoot dry biomass, shoot nutrient contents, mycorrhization, plant nitrate reductase (NR) and acid phosphomonoesterase activities, soil enzyme activities and aggregate stability. Ten months after field transplanting, it was found that the three experimental factors had interacted synergistically with regard to shoot and root biomass, with increases of about 410% and 370%, respectively relative to plants in the untreated soil. The treatment combining all three factors increased the root content of all heavy metals, and the levels of nitrogen (N), phosphorus, potassium and NR activity in shoot tissues, whereas it decreased root acid phosphomonoesterase activity. Soil dehydrogenase, protease and β-glucosidase activities, total N content and aggregate stability were increased by the combined treatment. In conclusion, the combination of the organic amendment, the native AM fungus and the native bacterium can be regarded as a suitable tool for phytostabilization with L. spartum due to its ability to enhance the tolerance of plants to heavy metals, improve the plant nutritional status and increase the soil microbial function related to the C cycling.

Alleviation of heavy metal stress and enhanced plant complex functional restoration in abandoned Pb–Zn mining areas by the nurse plant Coriaria nepalensis

Heavy metal pollution caused by mining has been a topic of concern globally because it threatens ecological functions and human health. Nearly all current remediation strategies take into account only such short-term issues as how to reduce or stabilize the content of heavy metals in soil, how to reduce the toxicity of heavy metals, and how to preserve water, soil and nutrients. However, little attention is paid to such long-term issues as whether plants can survive, whether communities can be stabilized, and whether ecosystem functions can be restored. Therefore, improving plant diversity and community stability are key aspects of improved mine restoration. To explore the possibility of reconstructing plant complexes in mining areas, the local nurse plant Coriaria nepalensis was selected as the research object for a study in the Huize Pb–Zn mining area of southwest China. C. nepalensis could increase the contents of nutrient elements (C, N, and P), reduce the contents of heavy metals (Mn, Cu, Zn, Cd, and Pb), and strengthen the plant complex functions (diversity, functional traits, and complex biomass) in its root zone. In general, C. nepalensis can form fertility islands (survival islands) in mining areas, which facilitate the colonization and success of additional less stress-resistant species. We propose C. nepalensis as a key species for use in restoration based on its ability to restore ecosystem functions under extremely stressful conditions. We encourage combination of C. nepalensis with other nurse plants to reinforce the rehabilitation of ecosystem functions.

A critical assessment on the short-term response of microbial relative composition in a mine tailings soil amended with biochar and manure compost

Phytomanagement of tailings requires the use of soil conditioners to favour plant establishment, but their benefits on soil microbial composition need to be assessed. The goal of this work was to evaluate the effect of two organic amendments, manure compost and biochar, on soil bacterial and fungal composition at metallic mine tailings. The addition of compost caused stronger effects in most of soil parameters and microbial composition than biochar, especially at the initial stage of the experiment. However, the higher dependence on labile organic carbon for some bacterial groups at the treatments containing compost determined their decay along time (Flavobacteriales, Sphingobacteriales) and the appearance of other taxa more dependent on recalcitrant organic matter (Xanthomonadales, Myxococcales). Biochar favoured bacterial decomposers (Actinomycetales) specialised in high lignin and other recalcitrant carbon compounds. Unlike bacteria, only a few fungal orders increased their relative abundances in the treatments containing compost (Sordariales and Microascales) while the rest showed a decrease or remained unaltered. The mix biochar-compost may result the best option to support a more diverse microbial population in terms of soil functionality that is able to decompose both labile and recalcitrant carbon compounds. This may favour the resilience of the system against environmental stressors.