| Soil heavy metal pollution is one of the major environmental problems in China,which has become a significant threat to ecological civilization and agricultural sustainable development.Among them,soil Pb pollution is more concerned than others because of its strong toxic effect,wide range of influence and frequent occurrence of security incidents.So it's urgent to abate pollution.In recent years,phytoremediation technology has been accepted widely because of its advantages of low price,being environmental friendly and in-situ remediation.Selecting suitable superrich plants is the basis of plant remediation application.However,there are few kinds of lead superrich plants defined and the low efficiency is also a problem.As a result,it has become an academic hot field to further explore the potential of plant restoration and improve the efficiency of plant antagonism and in-situ remediation.Pogonatherum crinitum,a kind of perennial plant in grass family,is a sort of Pb hyperaccumulator found and verified by our resarch group,which has strong Pb tolerance and enrichment capability.Results of previous studies showed that P.crinitum can realize the detoxification of Pb by root extension,improving the activity of internal antioxidant enzymes,eliminating reactive oxygen species and cell compartmentalization.With root system being an important interface of plants to contact with the soil,plant rhizosphere ecological effect,as the key part of affect plant growth and endurance strength,played an important role in adaption to soil Pb pollution of P.crinitum's.However,the mechanism of P.crinitum's adaption is still not clear,which severely limits the improvement of its application and efficiency remediation.Therefore,this paper designs experiments on some practical problems,such as the rhizosphere effect of Pb superrich plants,the improvement of antagonistic level and enrichment ability.So we use P.crinitum,a sort of Pb superrich plants,as material to understand its response to heavy metal stress at different Pb concentrations,including the growth morphology,lead accumulation and the antioxidant content of the root system,especially the differences in the variation of environmental factors,rhizosphere soil enzyme,rhizosphere soil Pb form,rhizosphere soil microbial diversity and community structure change under adverse circumstances.At the same time,in order to provide the reference for the resarch on Pb superrich plant anti-response,we analyzed the correlation between microenvironmental factor and its growth,to explore the response mechanisms of P.crinitum's environmental factors to heavy metal Pb stress and reveal P.crinitum's interactions between environmental regulation and its own detoxification strategy.The results are as follows:(1)With the increase of Pb concentration,the plant height,root morphology growth and biomass performs the tendency to promote later inhibition.Pb 1000 mg·kg-1 treatment promote the growth of the plant height,root length,root surface area,root mean diameter and root volume,and the plant biomass also reach the maximum.Under the treatment of Pb 3000 mg·kg-1,the growth of P.crinitum was significantly inhibited.The growth of the aboveground part and root systems decreased significantly.So is the biomass(P<0.05).However,under different Pb processing,the root average diameter were greater than comparison,while root-shoot ratio showed a trend of increase.This may be the situation that P.crinitum was sustaining root development and function and improve their resilience by adjusting the root growth pattern.(2)In different treatment of Pb concentration,the Pb content in the shoot and the root of P.crinitum was significantly higher than that in the control(P<0.05).In subcellular distribution,with the increase of Pb concentration,the proportion of F1 components of the root system was 57.7?77.3%,and the proportion of F1 components in the root system of P.crinitum was significantly increased(P<0.05).With the increase of the stress concentration,the cell shape and structure were damaged,and the suborganelles were badly damaged,while the cytoplasm and Pb particles deposited in the cell wall increased.It is speculated that the cell wall and soluble component are the two most important sites of Pb distribution of cells,and the separation of lead ions is an important mechanism for the detoxification of P.crinitum.(3)Pb stress has a significant effect on the synthesis of antioxidant substances and osmotic regulating substances.With the increase of stress concentration,the activity of SOD and POD in root decreased and MDA of root increased.The toxic effects of peroxidation are gradually revealed.However,the CAT activity of the root was first decreased and then increased,and the maximum value was reached at Pb 3000 mg·kg-1.Root GR activity,AsA and APX activity increased with stress concentration,all above control.At the same time,the content of SP and SS in the root system was higher than comparison while treated with Pb 2000?3000 mg·kg-1 and Pb 1000?2000 mg·kg-1 respectively.It can be found that the total antioxidant capacity of the root is enhanced by the increase of CAT activity in the root system within certain threshold,the regulation of ASA-GSH circulation and osmotic regulation.(4)Pb stress had little effect on the pH of non-rhizosphere soil,and the pH of rhizosphere decreased with the increase of stress concentration.Under Pb 3000 mg·kg-1 treatment,it was significantly lower than the control(P<0.05).P.crinitum's soil enzyme around roots has different sensitivities to soil under Pb stress.With concentration increasing,rhizosphere urease and acid phosphatase decreased after increased first,rhizosphere soil protease and sucrase overall decline.Under Pb 3000 mg·kg-1 treatment,the rhizoenzyme,urease and sucrase were significantly lower than the control(P<0.05).(5)The rhizospheric soil Pb form of P.crinitum was mainly composed of carbonate and manganese oxides.The percentage of exchangeable lead in rhizosphere soil of rhizosphere is lower than that of non rhizosphere,and the lead content of carbonate combined state in rhizosphere soil is higher than that in non rhizosphere,and the proportion is increasing.It indicates that the root of rhizosphere and rhizosphere of P.crinitum can reduce the exchangeable lead content that easily absorbed by plants,thus alleviating the harm of soil lead to plants.(6)The P.crinitum rhizospheric soil bacteria's Chao1,ACE index is higher than the contrast,shannon,simpon index is lower than the contrast under different Pb proceeding,showing that soil Pb processing will disturb and inhibit P.crinitum rhizospheric soil microbial diversity in certain degree.Lead-free and lead the rhizosphere bacteria on different levels are similar.Compared with the control,the relative abundance of the phylum Actinobacillus and the relative abundance of actinomycetes in the rhizosphere soil of Pb 1000?3000 mg·kg-1 increased and the relative abundance of actinomycetes decreased;at the level of the genus,the abundance of the genus comamonas and rhodanobacter was increased,and the Dyella facies decreased significantly.Through function prediction,under Pb treatment,patenting,partial dominant bacteria is closely related to P.crinitum rhizospheric soil growth resistance,cellular processes and environmental awareness,heavy metal transport,metabolism,ABC family,which has an positive effect on with P.crinitum's patience.(7)The results' reanalysis showed that there was a significant positive correlation between the soil urease and sucrose enzyme and the root growth and biomass;the Actinobacteria,SHA109,Acidobacteria and Cyanobacteria have a certain role in promoting the growth and soil enzyme and the activity of the root system.In addition,the Bacteroidetes,Actinobacteria,SHA109 and Firmicutes promoted the root SS,GR,ASA,GSH content and improved P.crinitum root osmotic regulation and antioxidant capacity.To sum up,under the condition of lead stress,the root growth and basic function can be maintained by the root mean diameter and the increase of root biomass.The root cell wall septum is used to limit the toxicity of lead ions,to induce antioxidant and osmotic substances to clear the excess reactive oxygen species in the root,and to improve the antioxidant capacity of the plant.At the same time,through the regulation of pH,enzyme activity and microbial bacteria in the rhizosphere soil,the rhizosphere effect of root growth and resistance can be strengthened,and the detoxification of lead can be realized so as to adapt to the environment with high concentration of lead stress. |
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