| The exploitation of coal resources can provide power resources for social infrastructure and economic development,but at the same time it causes environmental deterioration and land ecological damage in mining areas.Xinjiang Heishan open-pit coal mine is located in the continental arid and alpine climate zone.Due to extreme drought and poor soil,long-term coal mining has destroyed the vegetation and soil ecological environment of the dump.Therefore,it is urgent to explore environmentally friendly and economically feasible ecological restoration technologies.In this study,the characteristics of soil nutrients and vegetation community in mining dump were analyzed through field investigation,and the drought tolerance,phosphorus and potassium dissolving ability and metabolites of multifunctional actinomycetes isolated in extreme environment were studied.Inoculating local suitable plants with actinomycetes and in-situ pot experiments revealed the mechanism of actinomycetes enhancing drought tolerance of plants in arid mining areas from the perspectives of physiology,transcriptomics and metabonomics,and further revealed the promotion effect and restoration mechanism of actinomycetes on rhizosphere soil ecology from the perspective of soil enzyme physicochemical properties and macrogenomes,to provide theoretical basis and technical support for the ecological restoration of opencast coal mines in arid regions.The main results are as follows:（1）Through the ecological investigation and analysis of the mining dump,the results show that:（1）Eleven plant species have been investigated in the dump at different altitudes,and the natural restoration type of the mining dump is Agropyron cristatum)+Halogeton glomeratus)+Lepidium alashanicum community;With the altitude increasing,the species number first increased and then decreased,and there were more species at the altitude of 2553 m～2576 m.（2）At different altitudes,the spatial variation of soil factors in open-pit coal mine dump is great,and the total number of soil nutrients,enzyme activities and microorganisms first increases and then decreases with the increase of altitude.（3）The soil polyphenol oxidase increased significantly with the increase of altitude（P<0.05）,with the highest activity at 2632 m;The number of soil bacteria is the highest at 2560 m above sea level,and the number of fungi and actinomycetes is the highest at 2553 m above sea level.（4）Correlation analysis showed that the characteristic indexes of vegetation richness and community diversity were positively correlated with soil redox potential,microbial biomass carbon,soluble carbon,total nitrogen,soil polyphenol oxidase and soil bacteria.（2）In order to explore the strain characteristics of the tested actinomycetes,the drought tolerance,phosphorus and potassium dissolving abilities were tested.The results showed that:（1）Streptomyces pactum（SP）and Streptomyces rochei D74（SR）,were selected as the tested strains,and both of them had strong drought tolerance.（2）The solubility of two Streptomyces SP and SR to Ca3（PO4）2 reached 179.00 mg/L and501.10 mg/L respectively,and the solubility of SR to insoluble phosphate was stronger than that of SP strain.（3）With the increase of potassium feldspar powder,the potassium dissolution rate of SR is significantly higher than that of SP.（4）A variety of amino acids and their metabolites,carbohydrates and their metabolites are produced in the fermentation broth of SR,which can promote the drought resistance of plants.The results confirmed that SR not only has strong drought resistance,but also has the characteristics of plant growth promotion,so it can be selected as the in-situ test strain.（3）In-situ pot experiments were conducted to explore the effects of actinomycetes on the growth and drought resistance of plants in mining areas under drought conditions.The results showed that:（1）Inoculation with actinomycetes could significantly promote the growth and development of tested plants,ncreased the root phenotypes of Puccinellia distans and Onobrychis viciifolia,and improve the photosynthetic capacity of plants in mining areas.（2）Inoculation with actinomycetes significantly increased the soluble sugar content,proline content,glutathione content and antioxidant enzyme activity in leaves of Puccinellia distans and Onobrychis viciifolia,and at the same time decreased the malondialdehyde content in leaves of plants,alleviating the membrane damage and oxidative damage caused by drought.（3）RNA-Seq analysis identified 253differentially expressed genes（DEG）between leaves of Puccinellia distans inoculated with actinomycetes and those without actinomycetes under drought conditions.The in-depth analysis of these DEGs showed that actinomycetes regulated the expression of genes related to photosynthesis（LHC,Psb R,FBP and RPE）,sugar metabolism（EGLC,bgl X,ENO and pyk）,glutathione metabolism（DHAR,GST）and Ca2+signal transduction（RBOH）in plants under drought stress.（4）There were 198 different metabolites in leaves of Puccinellia distans inoculated with actinomycetes and uninoculated with actinomycetes,most of which were up-regulated,indicating that actinomycetes promoted the accumulation of protective substances such as antioxidation and cytoplasm by enhancing the osmotic adjustment ability of plants,thus enhancing their ability to resist drought stress.（4）In order to reveal the promotion effect and restoration mechanism of actinomycetes on the rhizosphere soil ecology of plants in the in-situ mining area under drought conditions,the physical and chemical properties and metagenome sequence of the rhizosphere soil of plants were determined.The results showed that:（1）actinomycetes could improve the physical properties of the rhizosphere soil of plants in the arid mining area,and the moisture content of rhizosphere soil of Puccinellia distans and Onobrychis viciifolia increased by 7.15%and 56.92%respectively after inoculation,and the redox potential of rhizosphere soil of Suaeda salsa decreased by 12.6%.（2）Inoculation with actinomycetes markly increased the nutrient content in rhizosphere soil of plants,and the soluble organic carbon content in rhizosphere soil of Puccinellia distans and Onobrychis viciifolia increased by 28.2%and 201.78%;The total nitrogen content increased by 9.2%and 166.27%respectively.The content of available potassium in rhizosphere soil of Onobrychis viciifolia inoculated with actinomycetes increased by 13.11%compared with that without inoculation.Compared with the control group,sucrase,urease activity and alkaline phosphatase activity in rhizosphere soil of Puccinellia distans and Onobrychis viciifolia increased by 94.20%and 31.82%,6.60%and 80.74%,64.63%and 85.02%respectively.（3）The total number of microorganisms,bacteria,fungi and actinomycetes in rhizosphere soil of plants treated with actinomycetes were significantly higher than those without inoculation.（4）The results of metagenome sequencing showed that inoculation with tested actinomycetes did not change the dominant community of soil bacteria,but actinomycetes increased the relative abundance of drought-tolerant microorganisms in plant inter-rhizosphere soils,with the dominant phyla including Actinomycetes,Ascomycetes,Acidobacteria,Bacteroidetes and Bacillariophyta. |
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