| Plant endophytes are consisted of fungi,bacteria and actinomyces which colonizating in plant tissue or organs without causing symptomatic infections or negative effects on their host.Plant endophytes could improve plants' growth and ability of tolerating abiotic stress through phosphate solubilization,solubilization of mineral,production of IAA and siderophores,utilization of 1-aminocyclopropane-1-carboxylic acid as a sole N source and transformation of nutrient elements,which indicate these species may play an important role in accelerating phytoremediation of metalliferous soils.Many studies have reported the plant-endophytes repairing of metalliferous soils,however,less of them have focused on this method in arid and semiarid regions.In this study,we explored the intensity of heavy metal soil pollution and assessed the plant's ability of heavy metal-enrichment in mining area,Gansu.We also separated plant endophytes to assess their diversities by constructing phylogenetic tree,then we selected heavy meatal-tolerance endophytes to measure their plant-growth-promoting characters and the ability of mineral solubilization,as well as compared the heavy meatal-tolerance ability of pair combination strains and single strain by comparing their growth curve in different concentrations of heavy metals.Finally,we determined the best endophytes according to stronger tolerance to Cu or Ni and owning more abilities of plant-growth-promoting and mineral solubilization.The results of this staudy are as follows:1.Jinchang has been seriously polluted by Cu and Ni.The concentration of Cu and Ni in the old tailing is respectively 96 times and 142 times than the soil background values of Jinchang.The pollution levels in Xipo is lower than the oldtailing,but the total concentration of Cu and Ni of Xipo is 5 times higher than the soil background values.2.The Ni absorption and Cu absorption of the aerial part of Anabasis aphylla grown in the old tailing was respectively up to 352.5±28.8mg/kg and 218.3±2.9mg/kg,which had the best ability to extract Cu and Ni in all the plants we collected,as well as the Cu and Ni translocation factor(TF)of Anabasis aphylla was respectively up to1.54 and 6.56.However the bioconcentration factor(BF)of this plant was less than 1.The plants grown in Xipo was lower in Ni absorption and Cu absorption but had a bigger TF.The biggest TF of Cu and Ni in Xipo was 1.22 and 1.03 belonging to the aerial part of Peganum harmala and Halogeton glomeratus respectively.3.We had gotten 44 strains from six plants and the analysis results of 16 S rDNA revealed that most of 40 strains,ruling out 4 strains failed to be identified,are affiliated to common genera,especially Bacillus,Pseudomonas and Microbacterium.There were 22.5% of the 40 strains belonging to the Pseudomonas,20% belonging to Bacillus and 15% of them identified as Microbacterium.In addition,there is only one article having reported a bacteria of Sinomicrobium separating from the mangrove plant,and we got the bacteria of Sphingobacterium from plant for the first time.Moreover HTC01 and WY03 maybe the potential new species of Sinomicrobium and Sphingobacterium respectively.By calculating the Shannon-Wiener index of plant endophyte of Laoweikuangba and Xipo,we fond that the former is bigger than the latter.4.Based on the Cu-MIC and Ni-MIC of 44 strains,we obtained eighteen Curesistant and Ni-resistant strains,in which JL10,JL05,WY01 and NN07 showed a strong tolerance against Ni,up to 7mM/L and WY09,NN01 and NN07 showed a strong tolerance against Cu,respectively up to 8mM/L,6mM/L and 6mM/L.5.By measuring the plant-growth-promoting characters including phosphate solubilization,production of IAA,ACC deaminase activity and solubilization of mineral,we fond that there were thirteen strains having the ability of phosphate solubilization,in which HTC02,NN01,JL01 and JL05 showed better capability of phosphate solubilization.What's more,all the strains could product IAA and higher concentration of IAA could be producted by HTC02,NN01,JL01 and JL05 than other strains.There were only three strains HWC01,WY01 and JL10 having the ACC deaminase activity.Most strains could mobilize copper and nickel in the soil,moreover NN06 and WY06 were outstanding in mobilizing Cu as well as NN05 and WY07 were easier to mobilize Ni than others.6.By comparing the inhibition rate of pair combination strains and single strain in different concentrations of heavy metals,we fond that the pair combination strains WY01-WY06 showed a stronger tolerance against Cu compared with other pair combination strains and single strain and pair combination strains NN01-NN07 a stronger tolerance against Ni than the others.Then,we came to the conclusion that the toxicity of Cu is higher than Ni for endophytic bacteria,so whether the growth difference between pair combination strains and single strain was significant or not depends on the concentration of Cu and Ni.That is to say the growth difference between pair combination strains NN01-NN07 and single strain NN01 had showed significant when the concentration of Cu is 100mg/l,while the growth difference between pair combination strains WY01-WY06 and single strain WY01 had just showed significant when the concentration of Ni is 300mg/l.In our study,we fond a endophytic bacteria belong to Sphingobacterium for the first time and we first separated a endophytic bacteria belonging to Sinomicrobium from a plant grown on the alpine and arid area.In addition,we fond that increase of heavy metal stress lead to the add of diversity of plant endophytes.Finally,we chose the pair combination strains NN01-NN07 and pair combination strains WY01-WY06 with pluripotentiality and stronger heavy metal-resistant tolerance as the optimal strains,providing good materials for plant and microbe combined remediation on Cu and Ni contaminated soil. |
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