Phytostabilization of Pb-Zn Mine Tailings with Amorpha fruticosa Aided by Organic Amendments and Triple Superphosphate

Recent trends in the phytoremediation of radionuclide contamination of soil by cesium and strontium: Sources, mechanisms and methods: A comprehensive review

This comprehensive review examines recent trends in phytoremediation strategies to address soil radionuclide contamination by cesium (Cs) and strontium (Sr). Radionuclide contamination, resulting from natural processes and nuclear-related activities such as accidents and the operation of nuclear facilities, poses significant risks to the environment and human health. Cs and Sr, prominent radionuclides involved in nuclear accidents, exhibit chemical properties that contribute to their toxicity, including easy uptake, high solubility, and long half-lives. Phytoremediation is emerging as a promising and environmentally friendly approach to mitigate radionuclide contamination by exploiting the ability of plants to extract toxic elements from soil and water. This review focuses specifically on the removal of 90Sr and 137Cs, addressing their health risks and environmental implications. Understanding the mechanisms governing plant uptake of radionuclides is critical and is influenced by factors such as plant species, soil texture, and physicochemical properties. Phytoremediation not only addresses immediate contamination challenges but also provides long-term benefits for ecosystem restoration and sustainable development. By improving soil health, biodiversity, and ecosystem resilience, phytoremediation is in line with global sustainability goals and environmental protection initiatives. This review aims to provide insights into effective strategies for mitigating environmental hazards associated with radionuclide contamination and to highlight the importance of phytoremediation in environmental remediation efforts.

Microplastics increase cadmium absorption and impair nutrient uptake and growth in red amaranth (Amaranthus tricolor L.) in the presence of cadmium and biochar

Microplastic (MP) pollution in terrestrial ecosystems is gaining attention, but there is limited research on its effects on leafy vegetables when combined with heavy metals. This study examines the impact of three MP types-polyethylene (PE), polyethylene terephthalate (PET), and polystyrene (PS)-at concentrations of 0.02, 0.05, and 0.1% w/w, along with cadmium (Cd) and biochar (B), on germination, growth, nutrient absorption, and heavy metal uptake in red amaranth (Amaranthus tricolor L.). We found that different MP types and concentrations did not negatively affect germination parameters like germination rate, relative germination rate, germination vigor, relative germination vigor, and germination speed. However, they increased phytotoxicity and decreased stress tolerance compared to an untreated control (CK1). The presence of MPs, particularly the PS type, reduced phosphorus and potassium uptake while enhancing Cd uptake. For example, treatments PS0.02CdB, PS0.05CdB, and PS0.1CdB increased Cd content in A. tricolor seedlings by 158%, 126%, and 44%, respectively, compared to the treatment CdB (CK2). Additionally, MP contamination led to reduced plant height, leaf dry matter content, and fresh and dry weights, indicating adverse effects on plant growth. Moreover, the presence of MPs increased bioconcentration factors and translocation factors for Cd, suggesting that MPs might act as carriers for heavy metal absorption in plants. On the positive side, the addition of biochar improved several root parameters, including root length, volume, surface area, and the number of root tips in the presence of MPs, indicating potential benefits for plant growth. Our study shows that the combination of MPs and Cd reduces plant growth and increases the risk of heavy metal contamination in food crops. Further research is needed to understand how different MP types and concentrations affect various plant species, which will aid in developing targeted mitigation strategies and in exploring the mechanisms through which MPs impact plant growth and heavy metal uptake. Finally, investigating the potential of biochar application in conjunction with other amendments in mitigating these effects could be key to addressing MP and heavy metal contamination in agricultural systems.

Optimizing biochar, vermicompost, and duckweed amendments to mitigate arsenic uptake and accumulation in rice (Oryza sativa L.) cultivated on arsenic-contaminated soil

The accumulation of arsenic (As) in rice (Oryza sativa L.) grain poses a significant health concern in Bangladesh. To address this, we investigated the efficacy of various organic amendments and phytoremediation techniques in reducing As buildup in O. sativa. We evaluated the impact of five doses of biochar (BC; BC0.1: 0.1%, BC0.28: 0.28%, BC0.55: 0.55%, BC0.82: 0.82% and BC1.0: 1.0%, w/w), vermicompost (VC; VC1.0: 1.0%, VC1.8: 1.8%, VC3.0: 3.0%, VC4.2: 4.2% and VC5.0: 5.0%, w/w), and floating duckweed (DW; DW100: 100, DW160: 160, DW250: 250, DW340: 340 and DW400: 400 g m- 2) on O. sativa cultivated in As-contaminated soil. Employing a three-factor five-level central composite design and response surface methodology (RSM), we optimized the application rates of BC-VC-DW. Our findings revealed that As contamination in the soil negatively impacted O. sativa growth. However, the addition of BC, VC, and DW significantly enhanced plant morphological parameters, SPAD value, and grain yield per pot. Notably, a combination of moderate BC-DW and high VC (BC0.55VC5DW250) increased grain yield by 44.4% compared to the control (BC0VC0DW0). As contamination increased root, straw, and grain As levels, and oxidative stress in O. sativa leaves. However, treatment BC0.82VC4.2DW340 significantly reduced grain As (G-As) by 56%, leaf hydrogen peroxide by 71%, and malondialdehyde by 50% compared to the control. Lower doses of BC-VC-DW (BC0.28VC1.8DW160) increased antioxidant enzyme activities, while moderate to high doses resulted in a decline in these activities. Bioconcentration and translocation factors below 1 indicated limited As uptake and translocation in plant tissues. Through RSM optimization, we determined that optimal doses of BC (0.76%), VC (4.62%), and DW (290.0 g m- 2) could maximize grain yield (32.96 g pot- 1, 44% higher than control) and minimize G-As content (0.189 mg kg- 1, 54% lower than control). These findings underscore effective strategies for enhancing yield and reducing As accumulation in grains from contaminated areas, thereby ensuring agricultural productivity, human health, and long-term sustainability. Overall, our study contributes to safer food production and improved public health in As-affected regions.

A critical review on the migration and transformation processes of heavy metal contamination in lead-zinc tailings of China

The health risks of lead-zinc (Pb-Zn) tailings from heavy metal (HMs) contamination have been gaining increasing public concern. The dispersal of HMs from tailings poses a substantial threat to ecosystems. Therefore, studying the mechanisms of migration and transformation of HMs in Pb-Zn tailings has significant ecological and environmental significance. Initially, this study encapsulated the distribution and contamination status of Pb-Zn tailings in China. Subsequently, we comprehensively scrutinized the mechanisms governing the migration and transformation of HMs in the Pb-Zn tailings from a geochemical perspective. This examination reveals the intricate interplay between various biotic and abiotic constituents, including environmental factors (EFs), characteristic minerals, organic flotation reagents (OFRs), and microorganisms within Pb-Zn tailings interact through a series of physical, chemical, and biological processes, leading to the formation of complexes, chelates, and aggregates involving HMs and OFRs. These interactions ultimately influence the migration and transformation of HMs. Finally, we provide an overview of contaminant migration prediction and ecological remediation in Pb-Zn tailings. In this systematic review, we identify several forthcoming research imperatives and methodologies. Specifically, understanding the dynamic mechanisms underlying the migration and transformation of HMs is challenging. These challenges encompass an exploration of the weathering processes of characteristic minerals and their interactions with HMs, the complex interplay between HMs and OFRs in Pb-Zn tailings, the effects of microbial community succession during the storage and remediation of Pb-Zn tailings, and the importance of utilizing process-based models in predicting the fate of HMs, and the potential for microbial remediation of tailings.

Status of Ecosystem Services in Abandoned Mining Areas in the Iberian Peninsula: Management Proposal

An abandoned sphalerite mining area in the southwest (SW) of the Iberian Peninsula was studied to evaluate the impact that the presence of metal(loid)s has on soil and ecosystem health. Five zones were delimited: sludge, dump, scrubland, riparian zone, and dehesa. Critical total levels of lead (Pb), zinc (Zn), thallium (Tl), and chromium (Cr), well above the limit indicative of toxicity problems, were found in the areas close to the sources of contamination. Pb-Zn concentrations were very high in the riparian zone, reaching values of 5875 mg/kg Pb and 4570 mg/kg Zn. The whole area is classifiable as extremely contaminated with Tl, with concentrations above 370 mg/kg in the scrubland. Cr accumulation mainly occurred in areas away from the dump, with levels up to 240 mg/kg in the dehesa. In the study area, several plants were found growing luxuriantly despite the contamination. The measured metal(loid)s content is the cause of a significant decrease in ecosystem services, resulting in unsafe soils for food and water production, so the implementation of a decontamination program is advisable. The plant species Retama sphaerocarpa, present in the sludge, scrubland, riparian zone, and dehesa, is postulated as suitable for use in phytoremediation.

Effect of Arbuscular Mycorrhiza Fungus Diversispora eburnea Inoculation on Lolium perenne and Amorpha fruticosa Growth, Cadmium Uptake, and Soil Cadmium Speciation in Cadmium-Contaminated Soil

Cadmium (Cd) pollution has become aggravated during the past decades of industrialization, severely endangering human health through its entry into the food chain. While it is well understood that arbuscular mycorrhizal fungi (AMF) have a strong ability to regulate plant growth and Cd uptake, studies investigating how they affect soil Cd speciation and influence Cd uptake are limited. We designed a pot experiment comprising two AMF-inoculant groups (inoculation with Diversispora eburnea or no inoculation), three Cd concentration levels (0, 5, and 15 mg/kg), and two plant species (Lolium perenne and Amorpha fruticosa) to study the effect of AMF Diversispora eburnea on plant growth, Cd uptake, and Cd speciation in the soil. The results revealed that L. perenne exhibited higher productivity and greater Cd uptake than A. fruticosa, regardless of AMF D. eburnea inoculation. However, AMF D. eburnea significantly altered soil Cd speciation by increasing the proportion of exchangeable Cd and decreasing residual Cd, resulting in Cd enrichment in the plant root organs and the elimination of Cd from the polluted soils. Our experiments demonstrate that inoculating plants with AMF D. eburnea is an effective alternative strategy for remediating Cd-contaminated soil.

An ecological remediation model combining optimal substrate amelioration and native hyperaccumulator colonization in non-ferrous metal tailings pond

The vegetation deterioration and pollution expansion from non-ferrous metal tailings pond have been found in many countries leading to water soil erosion and human health risk. Conventional ecological remediation technologies of mine tailings such as capping were costly and elusive. This study provided an economic and effective model as an alternative by substrate amelioration and vegetation restoration. A field experiment was carried out on a silver tailings pond in southwest China. Tailings substrate was ameliorated by adding organic matter (decomposed chicken manure, DCM), structural conditioner (polyacrylamide, PAM), water-retaining agent (acrylic acid-bentonite water-retaining agent, AAB), and heavy metal immobilizer (biofuel ash, BFA), which were optimized by laboratory experiment. Native heavy metal hyperaccumulator, Bidens pilosa, was colonized. Vegetation coverage and plant height of Bidens pilosa reached about 80% and over 30 cm respectively after 3 months, and the turbidity of tailings leaching solution decreased by 60%. The practice showed that the proportion of available heavy metals in tailings substrate was significantly lower than that in the soil surrounding mining area. Immobilization didn't have stabilization effect on Cd, Zn, and Pb, and As was only 0.002%, phytoremediation had stabilization effect of Cd, Zn, As, and Pb were 2.5-3.5%, 1-2%, 0.25-0.5%, and 0.25-0.75%. Phytoremediation was more effective significantly in controlling heavy metal pollution risk of tailings than immobilization. These results provided a new ecological remediation OSA-NHC model, meaning a combination of optimal substrate amelioration and native hyperaccumulator colonization, which could achieve vegetation restoration and augment heavy metal pollution control in non-ferrous metal tailings pond.

Temporal evolution of surface and sub-surface geochemistry and microbial communities of Pb-rich mine tailings during phytostabilization: A one-year pilot-scale study

Old mine waste repositories can present health and/or environmental issues linked to their erosion, inducing dissemination of metals and metalloids in air and water that can be attenuated through phytostabilization. Here, the effect of this widespread phytomanagement option on the biogeochemistry of a Pb-rich mine waste was evaluated with a laboratory pilot-scale experiment giving access to the non-saturated and saturated zones below the rhizosphere compartment. Amendment of the tailings surface with biochar, manure and iron-oxide-rich ochre promoted growth of the seeded Agrostis capillaris plants. These events were accompanied by an increase of pH and a decrease of Pb concentration in pore water of the surface layer, and by a transient increase of Pb, Zn, and Ba concentrations in the deeper saturated levels. Macroscopic and microscopic observations (SEM) suggest that Pb was immobilized in A. capillaris rhizosphere through mechanical entrapment of tailing particles. Microbial taxonomic and metabolic diversities increased in the amended phytostabilized surface levels, with a rise of the proportion of heterotrophic micro-organisms. Below the surface, a transient modification of microbial communities was observed in the non-saturated and saturated levels, however 11 months after seeding, the prokaryotic community of the deepest saturated zone was close to that of the initial tailings. pH and water saturation seemed to be the main parameters driving prokaryotic communities' structures. Results obtained at pilot-scale will help to precisely evaluate the impacts of phytostabilization on the temporal evolution of reactions driving the fate of pollutants inside the tailings dumps.

A review on invasive false indigo bush (Amorpha fruticosa L.): Nuisance plant with multiple benefits

Increased mobility of people around the globe has facilitated transferring species to new environments, where some have found suitable conditions and even become invasive. False indigo-bush (Amorpha fruticosa L.) is a plant native to North America but has intentionally or unintentionally spread over the Northern Hemisphere, where it often becomes invasive. The plant is especially easily dispersed within the watersheds of large rivers, where seasonal flooding is regular. Seeds and other propagules are buoyant, and when the water recedes, new plants emerge, forming dense thickets where only a few other species can co-exist. In order to sustain native biodiversity, spread control is needed. However, mechanical control and eradication measures currently in use are labor demanding and costly, while application of herbicides is limited. On the other hand, the plant possesses a number of beneficial properties, such as phytochemical applications (medical and insecticidal effects), biocoenotic uses (honey plant, ornamental features), and ecosystem services (soil stabilization, provision of food for animals, and fiber and biomass for industry, e.g., nanocellulose). For the reasons above mentioned, the plant is considered quite controversial, and the paper discusses both aspects: potential detrimental effects when introduced to new habitats and its beneficial uses for human society. In addition, the paper presents alternative measures of spreading control (e.g., grazing) and argues that exploiting it for beneficial purposes might help spread control, thus covering the expenses of controlling its distribution.

Biochar Alleviates Phytotoxicity by Minimizing Bioavailability and Oxidative Stress in Foxtail Millet (Setaria italica L.) Cultivated in Cd- and Zn-Contaminated Soil

Soil contamination with multiple heavy metals is a global environmental issue that poses a serious threat to public health and ecological safety. Biochar passivation is an efficient and economical technology to prevent heavy metal contamination of Cd; however, its effects on compound-contaminated and weakly alkaline soil remain unclear. Further, the mechanisms mediating the immobilization effects of biochar have not been evaluated. In this study, three biochar treated at different pyrolytic temperatures [300°C (BC300), 400°C (BC400), and 500°C (BC500)] were applied to Cd-/Zn-contaminated soils, and their effects on plant growth, photosynthetic characteristics, Cd/Zn accumulation and distribution in foxtail millet were evaluated. Further, the effect of biochar application on the soil physicochemical characteristics, as well as the diversity and composition of the soil microbiota were investigated. Biochar significantly alleviated the phytotoxicity of Cd and Zn. DTPA (diethylenetriamine pentaacetic acid)-Cd and DTPA-Zn content was significantly reduced following biochar treatment via the transformation of exchangeable components to stable forms. BC500 had a lower DTPA-Cd content than BC300 and BC400 by 42.87% and 39.29%, respectively. The BC500 passivation ratio of Cd was significantly higher than that of Zn. Biochar application also promoted the growth of foxtail millet, alleviated oxidative stress, and reduced heavy metal bioaccumulation in shoots, and transport of Cd from the roots to the shoots in the foxtail millet. The plant height, stem diameter, biomass, and photosynthetic rates of the foxtail millet were the highest in BC500, whereas the Cd and Zn content in each organ and malondialdehyde and hydrogen peroxide content in the leaves were the lowest. Moreover, biochar application significantly increased the abundance of soil bacteria and fungi, as well as increasing the fungal species richness compared to no-biochar treatment. Overall, biochar was an effective agent for the remediation of heavy metal-contaminated soil. The passivation effect of biochar exerted on heavy metals in soil was affected by the biochar pyrolysis temperature, with BC500 showing the best passivation effect.

Plant Growth-Promoting Bacteria (PGPB) integrated phytotechnology: A sustainable approach for remediation of marginal lands

Land that has little to no utility for agriculture or industry is considered marginal land. This kind of terrain is frequently found on the edge of deserts or other arid regions. The amount of land that can be used for agriculture continues to be constrained by increasing desertification, which is being caused by climate change and the deterioration of agriculturally marginal areas. Plants and associated microorganisms are used to remediate and enhance the soil quality of marginal land. They represent a low-cost and usually long-term solution for restoring soil fertility. Among various phytoremediation processes (viz., phytodegradation, phytoextraction, phytostabilization, phytovolatilization, phytofiltration, phytostimulation, and phytodesalination), the employment of a specific mechanism is determined by the state of the soil, the presence and concentration of contaminants, and the plant species involved. This review focuses on the key economically important plants used for phytoremediation, as well as the challenges to plant growth and phytoremediation capability with emphasis on the advantages and limits of plant growth in marginal land soil. Plant growth-promoting bacteria (PGPB) boost plant development and promote soil bioremediation by secreting a variety of metabolites and hormones, through nitrogen fixation, and by increasing other nutrients' bioavailability through mineral solubilization. This review also emphasizes the role of PGPB under different abiotic stresses, including heavy-metal-contaminated land, high salinity environments, and organic contaminants. In our opinion, the improved soil fertility of marginal lands using PGPB with economically significant plants (e.g., Miscanthus) in dual precession technology will result in the reclamation of general agriculture as well as the restoration of native vegetation.

Additions of optimum water, spent mushroom compost and wood biochar to improve the growth performance of Althaea rosea in drought-prone coal-mined spoils

Ecosystem degradation as a result of coal mining is a common phenomenon in various regions of the world, especially in arid and semi-arid zones. The implementation of appropriate revegetation techniques can be considered crucial to restore these degraded areas. In this regard, the additions of spent mushroom compost (SMC) and wood biochar (WB) to infertile and degraded soils have been reported to enhance soil fertility and plant growth under water (W) deficit conditions. However, the combined application of W, SMC and WB to coal mine degraded soils, to promote Althaea rosea growth and facilitate subsequent restoration, has not been explored yet. Hence, in the current study a pot experiment was carried out by growing A. rosea on coal mine spoils to assess the influence of different doses of W, SMC and WB on its morpho-physiological and biochemical growth responses. The results indicated that several plant growth traits like plant height, root length and dry biomass significantly improved with moderate W-SMC-WB doses. In addition, the simultaneous application of W-SMC-WB caused a significant decrease in hydrogen peroxide (H₂O₂) (by 7-56%), superoxide anion (O₂^●‒) (by 14-51%), malondialdehyde (MDA) (by 23-46%) and proline (Pro) contents (by 23-66%), as well as an increase in relative water content (by 10-27%), membrane stability index (by 2-24%), net photosynthesis rate (by 40-99%), total chlorophylls (by 43-113%) and carotenoids (by 31-115%), as compared to the control treatment. The addition of SMC and WB under low-W regime enhanced leaf water use efficiency, and soluble sugar content, also boosting the activity of superoxide dismutase, catalase, peroxidase and ascorbate peroxidase in leaf tissues, thus reducing the oxidative stress, as proved by low levels of H₂O₂, O₂^●‒, MDA and Pro contents. Finest growth performance under optimum doses of W (60% field capacity), SMC (1.4%) and WB (0.8%) suggest that revegetation of A. rosea with the recommended W-SMC-WB doses would be a suitable and eco-friendly approach for ecological restoration in arid degraded areas.

Composition and Properties of Triple Superphosphate Obtained from Oyster Shells and Various Concentrations of Phosphoric Acid

Triple superphosphates [TSPs, Ca(H₂PO₄)₂·H₂O] were produced by exothermic reactions of oyster shells and different concentrations of phosphoric acid (10, 20, 30, 40, 50, 60, and 70% w/w) in a molar ratio of 1:2. The percentage yields, P₂O₅ and CaO contents, metal impurities, and thermal behaviors of all the as-prepared products are dependent on the concentrations of phosphoric acid added during the production processes, which confirm to get the best optimum of 60% w/w phosphoric acid. All the as-prepared products were characterized by several characterization methods [X-ray fluorescence, thermal gravimetric/derivative thermal gravimetric analysis, powder X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy], verifying that all the obtained compounds are TSP that can be used as fertilizers without metal toxic contaminants. From the successful results, the method for TSP production can be applied in the fertilizer industry based on starting waste materials of oyster shells that can replace the use of unsustainable phosphate or calcium minerals obtained from nonliving things.

Carbonation, Cementation, and Stabilization of Ultramafic Mine Tailings

Tailings dam failures can cause devastation to the environment, loss of human life, and require expensive remediation. A promising approach for de-risking brucite-bearing ultramafic tailings is in situ cementation via carbon dioxide (CO₂) mineralization, which also sequesters this greenhouse gas within carbonate minerals. In cylindrical test experiments, brucite [Mg(OH)₂] carbonation was accelerated by coupling organic and inorganic carbon cycling. Waste organics generated CO₂ concentrations similar to that of flue gas (up to 19%). The abundance of brucite (2-10 wt %) had the greatest influence on tailings cementation as evidenced by the increase in total inorganic carbon (TIC; +0.17-0.84%). Brucite consumption ranged from 64-84% of its initial abundance and was mainly influenced by water availability. Higher moisture contents (e.g., 80% saturation) and finer grain sizes (e.g., clay-silt) that allowed for a better distribution of water resulted in greater brucite carbonation. Furthermore, pore clogging and surface passivation by Mg-carbonates may have slowed brucite carbonation over the 10 weeks. Unconfined compressive strengths ranged from 0.4-6.9 MPa and would be sufficient in most scenarios to adequately stabilize tailings. Our study demonstrates the potential for stabilizing brucite-bearing mine tailings through in situ cementation while sequestering CO₂.

Optimal water and fertilizer applications improve growth of Tamarix chinensis in a coal mine degraded area under arid conditions

Coal-mined areas are often associated with hostile environmental conditions where the scarcity of water and key nutrient resources negatively affect plant growth and development. In this study we specifically addressed how different combinations of water (W), nitrogen (N) and phosphorus (P) might affect morpho-physiological and biochemical attributes of a native shrub species, Tamarix chinensis, grown on coal mine spoils. Our results show that under greenhouse conditions the application of moderate-to-high doses of W, N and P considerably improved growth-associated parameters (i.e. plant height, stem diameter, dry weight), as well as gas-exchange parameters, photosynthetic pigment contents and leaf water status of T. chinensis. Under field conditions high W and low N, P doses led to significant increases in plant growth-associated traits, gas-exchange parameters and leaf water status. Plant growth was generally higher under greenhouse conditions mainly because seedlings faced multiple stress when growing under field conditions. Low W-regime, regardless of N-P additions, improved osmotic adjustments in leaf tissues and also boosted the activity of several antioxidant enzymes to reduce the oxidative stress associated with W scarcity under greenhouse conditions. Importantly, our study shows how maximum growth performance of T. chinensis under field conditions was achieved at W, N and P doses of 150 mm year^-1 , 80 kg ha^-1 and 40 kg ha^-1 , respectively. Our findings suggest that achieving optimal rates of W, N and P application is crucial for promoting the ecological restoration of coal-mined areas with T. chinensis under arid environmental conditions.

Contrasting effects of maize residue, coal gas residue and their biochars on nutrient mineralization, enzyme activities and CO2 emissions in sandy loess soil

Mismanagement of crop straw and coal gas residue threatens the atmosphere and the economy. Nevertheless, thermal-pyrolysis is an option for management that turns bio-waste into biochar; its viability and adoption by the public as soil amendments is dependent on the agronomic and environmental values compared between biochar and the raw materials. We undertook a 60-day short-term analysis to assess the impact of various wastes and biochars, as well as inorganic nutrients (N), on carbon dioxide (CO₂) fluxes, soil enzyme activities, soil fertility status, and microbial activities. There were eight treatments of soil amendments: without an amendment (CK), Nutrients (N), straw + nutrients (S+N), straw biochar + nutrients (SB+N), coal gas residue + nutrients (C+N), coal gas residue biochar + nutrients (CB+N), straw + straw biochar + nutrients (S+SB+N) and coal gas residue waste + coal gas residue biochar + nutrients (C+ CB +N). The results indicated that soil EC, pH, nitrate N (NO₃^–- N), SOC, TN and available K were significantly (p < 0.05) increased coal gas residue biochar and combined with coal fly ash as compared to maize straw biochar and combined with maize straw and N treatments. The higher concentrations of soil MBC and MBN activities were increased in the maize straw application, while higher soil enzyme activity such as, invertase, urease and catalase were enhanced in the coal fly ash derived biochar treatments. The higher cumulative CO₂ emissions were recorded in the combined applications of maize straw and its biochar as well as coal gas residue and its biochar treatment. Our study concludes, that maize straw and coal fly ash wastes were converted into biochar product could be a feasible substitute way of discarding, since land amendment and decreased CO₂ fluxes and positive changes in soil microbial, and chemical properties, and can be confirmed under long-term conditions for reduction of economical and environment issues.

Characterization of Retama sphaerocarpa microsymbionts in Zaida lead mine tailings in the Moroccan middle Atlas

In the Moroccan Middle Atlas, the tailings rich in lead and other metal residues, in the abandoned Zaida mining district, represent a real threat to environment and the neighboring villages' inhabitants' health. In this semi-arid to arid area, phytostabilisation would be the best choice to limit the transfer of heavy metals to populations and groundwater. The aim of this work was to characterize the bacteria that nodulate Retama sphaerocarpa, spontaneous nitrogen fixing shrubby legume, native to the Zaida mining area, with great potential to develop for phytostabilisation. Forty-three bacteria isolated from root nodules of the plant were characterized. Based on REP-PCR and ARDRA, four strains were selected for further molecular analyzes. The 16S rRNA gene sequences analysis revealed that the isolated strains are members of the genus Bradyrhizobium, and the phylogenetic analysis of the housekeeping genes glnII, atpD, gyrB, rpoB, recA and dnaK individual sequences and their concatenation showed that the strains are close to B. algeriense RST89^T and B. valentinum LmjM3^T with similarity percentages of 89.07% to 95.66% which suggest that the newly isolated strains from this mining site may belong to a potential novel species. The phylogeny of the nodA and nodC genes showed that the strains belong to the symbiovar retamae of the genus Bradyrhizobium. These strains nodulate also R. monosperma, R. dasycarpa and Lupinus luteus.

Fine-tuning of soil water and nutrient fertilizer levels for the ecological restoration of coal-mined spoils using Elaeagnus angustifolia

Coal mining activities remain of great environmental concern because of several negative impacts on soil ecosystems. Appropriate revegetation interventions of coal-spoiled lands can provide environmental management solutions to restore soil degraded ecosystems. The present study addressed the potential of the pioneer woody species, Elaeagnus angustifolia, in the restoration of coal-mined spoils under a range of different water (W) levels and nitrogen (N) and phosphorus (P) applications. Our results show how moderate applications of N (N₆₀ = 60 mg N kg^-1 soil) and P (P₉₀ = 90 mg P kg^-1 soil) fertilizers led either to maximum or minimum growth performance of E. angustifolia depending on whether W was applied at very high (W₈₀ = 80% field capacity) or very low (W₄₀ = 40% field capacity) levels suggesting that W was the main limiting factor for plant growth. Very low-W regime (W₄₀N₆₀P₉₀) also caused significant reduction of photosynthetic parameters, including net photosynthetic rate, transpiration rate and water use efficiency. The combination of high W-N doses with low P doses (W₇₀N₉₆P₃₆) positively influenced gas-exchange parameters, chlorophyll and carotenoid contents. Seedlings treated with low-W and -N doses (W₅₀N₂₄P₁₄₄) showed highest increases in malondialdehyde content and lowest levels of relative water content (RWC). Decreases in malondialdehyde content and increases in RWC were observed following a gradual increment of W and N doses, indicating that high W and N doses contributed to drought tolerance of E. angustifolia by protecting cell membranes and increasing water status. Low-W and -N applications considerably increased the activities of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase) and the contents of proline and soluble sugars, suggesting that E. angustifolia developed defensive strategies to avoid damage induced by water scarcity. Results from heatmap and principal component analyses confirmed that W and N were the main clustering factors, and both N and P performed well at high-W dose. The optimum growth performance of E. angustifolia was found under a combination of W level at 66.0% of field capacity, N dose of 74.0 mg kg^-1 soil, and P dose of 36.0 mg kg^-1 soil. Our findings demonstrate how optimum growth performance of E. angustifolia can be achieved by fine-tuning doses of W, N, and P resources, and how this in turn could greatly support the ecological restoration of coal-mined degraded environments.

Exogenous Melatonin Modulates the Physiological and Biochemical Mechanisms of Drought Tolerance in Tartary Buckwheat (Fagopyrum tataricum (L.) Gaertn)

Tartary buckwheat is one of the nutritious minor cereals and is grown in high-cold mountainous areas of arid and semi-arid zones where drought is a common phenomenon, potentially reducing the growth and yield. Melatonin, which is an amphiphilic low molecular weight compound, has been proven to exert significant effects in plants, under abiotic stresses, but its role in the Tartary buckwheat under drought stress remains unexplored. We evaluated the influence of melatonin supplementation on plant morphology and different physiological activities, to enhance tolerance to posed drought stress by scavenging reactive oxygen species (ROS) and alleviating lipid peroxidation. Drought stress decreased the plant growth and biomass production compared to the control. Drought also decreased Chl a, b, and the Fv/Fm ratio by 54%, 70%, and 8%, respectively, which was associated with the disorganized stomatal properties. Under drought stress, H2O2, O2•-, and malondialdehyde (MDA) contents increased by 2.30, 2.43, and 2.22-folds, respectively, which caused oxidative stress. In contrast, proline and soluble sugar content were increased by 84% and 39%, respectively. However, exogenous melatonin (100 µM) could improve plant growth by preventing ROS-induced oxidative damage by increasing photosynthesis, enzymatic antioxidants (superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase), secondary metabolites like phenylalanine ammonialyase, phenolics, and flavonoids, total antioxidant scavenging (free radical DPPH scavenging), and maintaining relative water content and osmoregulation substances under water stress. Therefore, our study suggested that exogenous melatonin could accelerate drought resistance by enhancing photosynthesis and antioxidant defense in Tartary buckwheat plants.