Synergistic effect of organo-mineral amendments and plant growth-promoting rhizobacteria (PGPR) on the establishment of vegetation cover and amelioration of mine tailings

Mine tailings pose a huge hazard for environmental and human health, and the establishment of vegetation cover is crucial to reduce pollutant dispersion for the surroundings. However, their hostile physicochemical conditions hamper plant growth, compromising phytoremediation strategies. This study aims to investigate the role of organo-mineral amendments and plant growth-promoting rhizobacteria (PGPR) on the improvement of mine tailings properties and Lolium perenne L. (ryegrass) growth. Plants were grown in mine tailings mixed with an agricultural soil (1:1), 10% compost, and supplied with two different inorganic amendments – rock phosphate (6%) or lime (3%), and inoculated with the rhizobacterial strains Advenella kashmirensis BKM20 (B1) and Mesorhizobium tamadayense BKM04 (B2). The application of organo-mineral amendments ameliorated tailings characteristics, which fostered plant growth and further enhanced soil fertility and microbial activity. These findings were consistent with the increase of total organic carbon levels, with the higher numbers of heterotrophic and phosphate solubilizing bacteria, and higher dehydrogenase and urease activities, found in these substrates after plant establishment. Plant growth was further boosted by PGPR inoculation, most noticeable by co-inoculation of both strains. Moreover, inoculated plants showed increased activities for several antioxidant enzymes (catalase, peroxidase, polyphenoloxidase, and glutathione reductase) which indicate a reinforced antioxidant system. The application of agricultural soil, compost and lime associated with the inoculation of a mixture of PGPR proved to enhance the establishment of vegetation cover, thus promoting the stabilization of Kettara mine tailings. Nonetheless, further studies are needed in order to confirm its effectiveness under field conditions.info:eu-repo/semantics/acceptedVersio

Physical, chemical, and microbiological characterization of Kettara Mine Tailings, Morocco

The mining industry is of major importance to Morocco’s economy. However, the abandoned pyritic mines are a source of potentially toxic elements that can cause the disruption of the surrounding ecosystems, constituting a huge threat to wellbeing and human health. The present study aimed to analyze the physical and chemical characteristics of different types of tailings and to investigate the microbial populations of acidophilic bacteria involved in the oxidation of pyrite. Coarse and fine tailings collected from different zones of the mine (dike and pond) at two different depths (oxidized and non-oxidized residues) were analyzed for their pH, electrical conductivity, total organic carbon, total nitrogen, available P, major elements, and pseudo-total metal concentrations. The abundance of acidophilic bacteria was determined, and some acidophilic bacterial strains were isolated and tested for their metal tolerance. Tailings showed a pH ≈ 2, very low nutritional content, and high concentrations of Cu, As, Zn, and Pb, which were higher in the non-oxidized samples. The microbial counts of iron- and sulfur-oxidizing bacteria were higher than heterotrophic bacteria, with the highest numbers detected in the oxidized fine tailings. The five acidophilic bacteria isolated from the tailings were affiliated to genera Alicyclobacillus and Sulfobacillus, commonly found in this kind of environment.info:eu-repo/semantics/publishedVersio

Enhancing native plant establishment in mine tailings under drought stress conditions through the application of organo-mineral amendments and microbial inoculants

The implementation of phytoremediation strategies under arid and semiarid climates requires the use of appropriate plant species capable of withstanding multiple abiotic stresses. In this study, we assessed the combined effects of organo-mineral amendments and microbial inoculants on the chemical and biological properties of mine tailings, as well as on the growth of native plant species under drought stress conditions. Plants were cultivated in pots containing 1 kg of a mixture of mine tailings and topsoil (i.e., pre-mined superficial soil) in a 60:40 ratio, 6% marble sludge, and 10% sheep manure. Moreover, a consortium of four drought-resistant plant growth-promoting rhizobacteria (PGPR) was inoculated. Three irrigation levels were applied: well-watered, moderate water deficit, and severe water deficit, corresponding to 80%, 45%, and 30% of field capacity, respectively. The addition of topsoil and organo-mineral amendments to mine tailings significantly improved their chemical and biological properties, which were further enhanced by bacterial inoculation and plants’ establishment. Water stress negatively impacted enzymatic activities in amended tailings, resulting in a significant decrease in acid and alkaline phosphatases, urease, and dehydrogenase activities. Similar results were obtained for bacteria, fungi, and actinomycete abundance. PGPR inoculation positively influenced the availability of phosphorus, total nitrogen, and organic carbon, while it increased alkaline phosphatase, urease (by about 10%), and dehydrogenase activity (by 50%). The rhizosphere of Peganum harmala showed the highest enzymatic activity and number of culturable microorganisms, especially in inoculated treatments. Severe water deficit negatively affected plant growth, leading to a 40% reduction in the shoot biomass of both Atriplex halimus and Pennisetum setaceum compared to well-watered plants. P. harmala showed greater tolerance to water stress, evidenced by lower decreases observed in root and shoot length and dry weight compared to well-watered plants. The use of bioinoculants mitigated the negative effects of drought on P. harmala shoot biomass, resulting in an increase of up to 75% in the aerial biomass in plants exposed to severe water deficit. In conclusion, the results suggest that the combination of organo-mineral amendments, PGPR inoculation, and P. harmala represents a promising approach to enhance the phytoremediation of metal-polluted soils under semiarid conditions.info:eu-repo/semantics/publishedVersio

Assessment of plant growth promoting bacterial populations in the rhizosphere of metallophytes from the Kettara mine, Marrakech

Soil heavy metal contamination resulting from mining activities constitutes a major environmental problem worldwide. The spread of heavy metals is often facilitated by scarce vegetation cover, so there is an urgent need to improve plant survival and establishment in these metalliferous areas. This study is aimed at the isolation and analysis of the phylogenetic relationship of culturable bacteria from the rhizosphere of metallophyte plants growing in the Kettara mine, in Marrakech, in order to select plant growth-promoting rhizobacteria (PGPR), which could be used in assisted-phytoremediation. Bacterial isolates were grouped by random amplified polymorphic DNA analysis and identified by 16S rRNA gene sequencing. Strains were further characterized for the production of plant growth-promoting (PGP) substances, such as NH3, siderophores, indol-3-acetic acid (IAA), hydrogen cyanide, and extracellular enzymes, for ACC-deaminase activity, their capacity to solubilize phosphate, and for their tolerance to heavy metals and acidic pH. Rhizosphere soils were highly contaminated with Cu and Zn and presented low fertility. Phylogenetic analysis showed that the rhizobacteria were affiliated to three major groups: γ-Proteobacteria (48 %), β-Proteobacteria (17 %), and Bacilli (17 %). The most represented genera were Pseudomonas (38 %), Bacillus (10 %), Streptomyces (10 %), and Tetrathiobacter (10 %). Overall, rhizobacterial strains showed an ability to produce multiple, important PGP traits, which may be helpful when applied as plant growth promoter agents in contaminated soils. PGPR were also able to withstand high levels of metals (up to 2615.2 mg Zn l(-1), 953.29 mg Cu l(-1), and 1124.6 mg Cd l(-1)) and the order of metal toxicity was Cd > Cu > Zn. The rhizobacterial strains isolated in the present study have the potential to be used as efficient bioinoculants in phytoremediation strategies for the recovery of Kettara mine soils.info:eu-repo/semantics/publishedVersio

Enzymes of the glutathione-ascorbate cycle in leaves and roots of rhizobia-inoculated faba bean plants (<em>Vicia faba</em> L.) under salinity stress.

Grain legumes such as the faba bean (Vicia faba L.) used for human as well as animal nutrition, are of great importance especially in countries under Mediterranean climate like Morocco, which is mainly characterized by semi-arid and arid climates and by saline soils. The objective of the present study was to evaluate the effects of salt stress on growth, nodulation and the enzymes of the glutathione ascorbate cycle of faba bean plants (Moroccan cultivar &quot;Aguadulce&quot;). The experiments were carried out under greenhouse-conditions, where faba bean plants were grown under control (nutrient solution) or salt stress conditions (nutrient solution containing 75 mM or 150 mM of NaCl). The activity of enzymes of the glutathione ascorbate cycle was studied in leaves and roots of faba bean plants inoculated by rhizobia RhOF4 or RhOF6, isolated from nodules of faba bean cultures in the region of Marrakech. The growth of faba bean plants decreased with increasing salt concentrations. Total weight and length of shoots significantly decreased under NaCl stress (p &lt; 0.05), especially at 150 mM. Also the nodulation of the roots was strongly decreased under salinity stress, with reductions of 91.35% and of 88.67% in the total nodule number of plants exposed to 150 mM of NaCl and inoculated by RhOF4 and by RhOF6 respectively. NaCl effects on the glutathione-ascorbate cycle were more pronounced in roots inoculated by RhOF6. Stress responding glutathione S-transferase (GST) activity was generally increased in roots inoculated by RhOF6 and submitted to salt stress. On the contrary, specific activities of glutathione peroxidase (GPOX), superoxide dismutase (SOD), ascorbate peroxidase (APOX) and monodehydroascorbate reductase (MDHAR) were reduced in roots of faba bean plants inoculated by RhOF6 exposed to saline treatment as compared to the controls. Our results show the importance of several enzymes of the ascorbate-glutathione cycle and the reduced glutathione (GSH) during some faba bean-rhizobia symbiotic combinations, in root defence and adaptation against salt stress conditions. (C) 2013 Elsevier Masson SAS. All rights reserved

Do metal contamination and plant species affect microbial abundance and bacterial diversity in the rhizosphere of metallophytes growing in mining areas in a semiarid climate?

Purpose Mining areas are low-quality habitats for macro- and microorganisms' development, mainly due to the degradation of the soil quality by metal pollution. The present work aimed to analyze the influence of metal contamination and of plant species on the rhizospheric microbial communities of four indigenous metallophytes (Ononis natrix, Haloxylon scoparium, Peganum harmala, and Aizoon canariense) growing along a metal contamination gradient in Kettara mine near Marrakech, Morocco. Materials and methods In pyrrhotite mining areas (Kettara mine, Morocco), rhizosphere soil samples were collected from four predominant indigenous metallophytes (O. natrix, H. scoparium, P. harmala, and A. canariense) growing along a metal contamination gradient (ZC, control zone; Z1, high metal contamination; Z2, moderate metal contamination; Z3, low metal contamination). Microbial communities were analyzed by using microbial counts and by denaturing gradient gel electrophoresis (DGGE). The physicochemical properties (pH, conductivity, total organic carbon, nitrogen, P Olsen, and metal concentrations) of soils were also determined. Results and discussion The physicochemical analysis revealed that rhizospheric soils from Z1, Z2, and Z3 were relatively poor in nutrients as they presented low levels of total organic carbon and nitrogen, organic matter and available P. Moreover, these rhizospheric soils showed high concentrations of metals, especially Cu and Pb, which significantly reduced the abundance of the different groups of soil microorganisms (bacteria, fungi, and actinomycetes) and the activity of soil dehydrogenase. The analysis of bacterial communities by DGGE revealed that bacterial diversity was not negatively affected by metal contamination being higher in the most contaminated area (Z1). Conclusions Overall, the microbial abundance, the composition, and the diversity of rhizospheric bacterial communities were more influenced by the environmental factors in sampling zones than by plant cover. Microbial counts and enzymatic activity were both systematically affected throughout the metal gradient, evidencing as good indicators of the harmful effects of anthropogenic disturbances in soils. H. scorparium and P. harmala proved to be good candidates for the development of phytotechnological programs aiming the revegetation of mining degraded areas.N/

Enhancing Native Plant Establishment in Mine Tailings under Drought Stress Conditions through the Application of Organo-Mineral Amendments and Microbial Inoculants

The implementation of phytoremediation strategies under arid and semiarid climates requires the use of appropriate plant species capable of withstanding multiple abiotic stresses. In this study, we assessed the combined effects of organo-mineral amendments and microbial inoculants on the chemical and biological properties of mine tailings, as well as on the growth of native plant species under drought stress conditions. Plants were cultivated in pots containing 1 kg of a mixture of mine tailings and topsoil (i.e., pre-mined superficial soil) in a 60:40 ratio, 6% marble sludge, and 10% sheep manure. Moreover, a consortium of four drought-resistant plant growth-promoting rhizobacteria (PGPR) was inoculated. Three irrigation levels were applied: well-watered, moderate water deficit, and severe water deficit, corresponding to 80%, 45%, and 30% of field capacity, respectively. The addition of topsoil and organo-mineral amendments to mine tailings significantly improved their chemical and biological properties, which were further enhanced by bacterial inoculation and plants’ establishment. Water stress negatively impacted enzymatic activities in amended tailings, resulting in a significant decrease in acid and alkaline phosphatases, urease, and dehydrogenase activities. Similar results were obtained for bacteria, fungi, and actinomycete abundance. PGPR inoculation positively influenced the availability of phosphorus, total nitrogen, and organic carbon, while it increased alkaline phosphatase, urease (by about 10%), and dehydrogenase activity (by 50%). The rhizosphere of Peganum harmala showed the highest enzymatic activity and number of culturable microorganisms, especially in inoculated treatments. Severe water deficit negatively affected plant growth, leading to a 40% reduction in the shoot biomass of both Atriplex halimus and Pennisetum setaceum compared to well-watered plants. P. harmala showed greater tolerance to water stress, evidenced by lower decreases observed in root and shoot length and dry weight compared to well-watered plants. The use of bioinoculants mitigated the negative effects of drought on P. harmala shoot biomass, resulting in an increase of up to 75% in the aerial biomass in plants exposed to severe water deficit. In conclusion, the results suggest that the combination of organo-mineral amendments, PGPR inoculation, and P. harmala represents a promising approach to enhance the phytoremediation of metal-polluted soils under semiarid conditions

Proyecto ReCROP: mejorando la diversidad microbiana del suelo en agroecosistemas mediterráneos

info:eu-repo/semantics/publishedVersio

Proyecto ReCROP: mejorando la diversidad microbiana del suelo en agroecosistemas mediterráneos

info:eu-repo/semantics/publishedVersio