| Plenty of pollutants(e.g heavy metal and organic pollutants)were emitted to the environment along with the industrial and agricultural activities,posing a great threat to the ecosystem and human health.The bioremediation associated with plant and microbe exhibits broad application prospect in heavy metals and organic pollutants co-contaminated soils.To ensure the success of remediation,it is very crucial that the plants and microbes survive under the heavy metal stress.Plants being capable of tolerating or hyper-accumulating heavy metals can not only alleviate the heavy metal pollution,but also protect microbes from the toxicity of heavy metal,which enable microbes to degrade organic pollutants more efficiently.Elsholtzia splendens,a native Cu tolerant plant in China,has potential application in the remediation of heavy metal contamination.However,its influence on microbes in co-contaminated soil,especially the organic pollutant degraders,is still unclear.To characterize the microbial community in E.splendens rhizosphere,reveal the influence of E.splendens on organic pollutants degraders,disclose the degradation mechanism and provide new insight for the application of E.splendens in the remediation of co-contaminated soils,we carried out the present study including pot experiments and field investigation.The major findings are in the following:Soils mixed with phenathrene,PCB-28 and different Cu(0,500,1000,1500 mg/kg)were used in pot experiments.For E.splendens,the leaves turned prunosus,the plant height and root became shorter in soils with more than 500 mg/kg Cu compared to the control group.But when soil Cu reached 1500 mg/kg,the plant height only decreased by 34.6%.However,for L.perenne,it turned into yellow and became short when Cu was higher than 500 mg/kg and the plant height decreased by 70%when Cu concentration reached 1500 mg/kg,which indicated that E.splendens was more tolerant to Cu than L.perene.No significant differences were observed for the content of MDA,SOD,POD and CAT between E.splendens and L.perenne in control groups.But in soils with the highest Cu concentration(1500 mg/kg),the content of MDA,SOD,POD and CAT in E.splendens was much lower than that in L.perenne.To explore the influence of E.splendens on microbes,we investigated the microbial communities in the rhizosphere of E.splendens and L.perenne based on next generation sequencing.In total,42 rare phyla and 9 dominant phyla(>1%)(Proteobacteria,Acidobacteria,Actinobacteria,Planctomycetes.Verrucomicrobia.Chloroflex,Cyanobacteria,Bacteroidetes and Chlamydiae)were identified in all samples.E.splendens planting changed the abundance of Actinobacteria,Cyanobacteria,Bacteroidetes(p<0.05)and only increased Bacteroidetes abundance in comparison to that in the rhizosphere of L.perenne.It was reported Bacteroidetes was resistant to Cu and might be related to Cu tolerance of E.splendens.At 97%OTU level,19 OTUs were enriched in E.splendens rhizosphere(>2 times;p<0.05)with Cu concentration higher than 1000 mg/kg.Among them,5 OTUs were still enriched in E.splendens rhizosphere when Cu concentration was less than 500 mg/kg,which indicated these OTUs were related to specific plant species rather than Cu and might play an important role in E.splendens tolerance to Cu.Among all of the environmental factors,Cu was the most important factor affecting the microbial communities construction.However,The extent of Cu impact varied with plant,which explained 12.6%,17.8%and 18.2%of the community variation in the soil of E.splendens rhizosphere,L.perenne rhizosphere and control soil,respectively.The ecological network of microbial communities revealing the relationship among microbes and high modularity indicated the stable community structure.We found that the modularity index decreased by 16.1%when Cu concentration increased from 0 to 1500 mg/kg.Compared with the control soils,the modularity index of microbial ecological network increased by 24.8%in E.splendens rhizosphere.Besides,the microbial quantity decreased by 34.9%and 35.1%in L.perenne rhizosphere compared with the control when soil Cu reached 1500 mg/kg.The quantity only decreased by 10.2%in E.splendens rhizosphere indicating that microbes in E.spendens rhizosphere were more tolerant to Cu.To understand the influence of E.splendens on organic pollutants degraders,stable isotope probing technique was applied to identify the degraders in soils amended with phenanthrene and PCB-28.We identified 41 phenanthrene degraders and 3 PCB-28 degraders.At low Cu concentration(?500 mg/kg),E.splendens did not change the degraders'abundance,but L.perenne decreased the degrader's abundance represented by OTU 70729(Family:Xanthomonadaceae).At high Cu concentration(? 1000 mg/kg),E.splendens increased the abundance of 2 degraders,but L.perenne hardly influence the degraders abundance.Furthermore,we studied the influence of E.splendens on rhizospheric xenobiotic-degrading genes.In samples with high Cu concentration,E.splendens and L.perenne significantly altered the gene abundance(? 1000 mg/kg)(p<0.05)with increased gene abundance in the rhizosphere of E.splendens and decreased gene abundance in the rhizosphere of L.perenne.Besides,the degradation rate of phenathrene and PCB-28 was higher in E.splendens rhizosphere than in L.perenne rhizosphere.Hence,we infer that E.splendens could improve the removal of organic pollutants in co-contamination sites.We further investigated the microbial community in the E.splendens rhizosphere in field.Twenty-one E.splendens rhizospheric soil samples with different Cu concentrations were collected from three Cu mines located in Tongling city in Anhui Province,Zhuji city in Zhejiang Province,and Nanjing city in Jiangsu Province.The 47 phyla including 11 dominant phyla(>1%)in E.splendens rhizosphere were identified:Proteobacteria,Actinobacteria,Chloroflexi,Verrucomicrobia,Acidobacteria,Bacteroidetes,Planctomycetes,Cyanobacteria,Firmicutes,Gemmatimonadetes and TM7.The relative abundance of Bacteroidetes was 6.4%,which was enriched in E.splendens rhizosphere in pot experiment.The 4 OTUs enriched in pot experiment still existed in E.splendens rhizospheric soil derived from field,and Cu affected their abundance slightly.It indicated that the Cu tolerant microbes in E.splendens rhizosphere were affected not only by plant species but also by soil type.The phyla abundances were affected by the environmental factors with different extent,Cu had little influence on bacterial community,which was different from pot experiment.It was speculated that E.splendens could alleviate the toxicity of Cu and microbes were adaptive in soil contaminated by Cu for a long time.In conclusion,the microbes in E.splendens rhizosphere were more tolerant to Cu.Besides,E.splendens improved the microbial abundance responsible for the degradation of organic pollutants and xenobiotic-degrading genes,which could benefit the dissipation of organic pollutants.E.splendens possesses a potential in the remediation of co-contaminated soils. |
PDF Full Text Request