| Heavy metal pollution in soil caused by metal mining has always been the focus of mine ecological remediation research.Phytoremediation,as an effective remediation technology for site pollution,has always been the first choice for the remediation of metal mine waste dump.Neyraudia reynaudiana is a common heavy metal pollution remediation plant,which has a wide range of growth in China and has been widely used.However,the field investigation found that there are differences in the site adaptability of Neyraudia reynaudiana,which indicates that the internal mechanism of Neyraudia reynaudiana remediation of heavy metal pollution needs to be further explored,the control factors of remediation ability need to be studied,and the influencing factors of remediation effect need to be explored.Therefore,firstly,through the field investigation and comparative analysis of metal mine reclamation waste dump,this thesis finds out the variation characteristics of soil heavy metal content and the difference of remediation effect by cultivated Neyraudia reynaudiana.Then carry out indoor heavy metal gradient concentration stress test to explore the ability of Neyraudia reynaudiana to enrich heavy metals in the whole growth cycle,the influencing factors of soil remediation effect and the physiological response mechanism of plants.Next,by quantitatively measuring the activities and statistical analysis of superoxide dismutase(SOD),catalase(CAT),ascorbic acid peroxidase(APX),glutathione reductase(GR)and peroxidase(POD)in the process of reed like response to oxidative stress,the mechanism of reed like absorption of heavy metals was revealed from the perspective of enzyme metabolic cycle.The main conclusions are as follows:(1)Field investigation and sampling test analysis found that Neyraudia reynaudiana was an effective remediation plant for soil heavy metal pollution,but there were differences in site adaptability.In the site rehabilitated for 10 years,when there was no significant difference in the initial soil lead(Pb),Chromium(Cr)and cadmium(Cd)contents,the contents of Pb and Cd in Neyraudia reynaudiana were significantly higher than those in Agave sisalana and other plants,with Pb enrichment rate of 1.05 and Cd enrichment rate of 3.83,but Cr enrichment capacity was not significant,only0.05.In the area rehabilitated for 17 years,the enrichment rate of Neyraudia reynaudiana about Cd was 6.75,which was significantly higher than that of other plants,and the enrichment rate of Pb was 1.04,which was not significantly different from that of 10-year restoration area,but the enrichment rate of Cr was 0.43.This indicates that there are differences in the adsorption capacity of Neyraudia reynaudiana for soil heavy metals,which provides a factual basis for the further study of the causes and mechanism of such differences.(2)The results of indoor heavy metal gradient concentration stress simulation test showed that there were differences in the ability of Neyraudia reynaudiana to enrich different heavy metals at different growth stages.The remediation effect of Neyraudia reynaudiana on Pb pollution in soil first increased and then decreased with the growth time.The higher the concentration,the shorter the peak time and the faster the decline;The rehabilitation effect of Neyraudia reynaudiana on Cr increased monotonously with the increase of growth time,and there was no obvious inflection point,but the increase rate slowed down.The restoration of Cd by Neyraudia reynaudiana will gradually decrease after reaching the peak within 120 days,but it has good adaptability to different concentrations of stress.Neyraudia reynaudiana has a strong ability to adsorb Cd,even at the high concentration of 1.0 mg/kg.(3)The results of indoor stress test showed that the concentration of heavy metals had a feedback effect on the adsorption capacity of Neyraudia reynaudiana,but the sensitivity of different heavy metals was different.Under low concentration stress,the enrichment ability of Neyraudia reynaudiana to Pb is very strong,but when the concentration exceeds 800 mg/kg,the enrichment rate decreases significantly and even dies.Neyraudia reynaudiana is not sensitive to the concentration of Cr.even under the stress of 1000 mg/kg,the rehabilitation ability remains good,indicating that Neyraudia reynaudiana is not sensitive to Cr pollutants.There have few changes of the enrichment ability of Neyraudia reynaudiana to Cd with the increase of concentration and can maintain good stability.(4)The analysis of enzyme activities in coping with oxidative stress showed that the enrichment of heavy metals in Neyraudia reynaudiana was mainly realized by enzyme activities in the body,which determined the absorption capacity of Neyraudia reynaudiana,and the activity levels of different enzymes were different at each growth stages and under different concentrations of stress.SOD,CAT,APX and POD firstly acted in the early stage of REDOX reaction,and GR REDOX system would continue to play a role when pollution intensified or the growth of Neyraudia reynaudiana entered the middle and late stage.The activity of SOD enzyme was relatively higher under Pb and Cd stress in the early growth stage of Neyraudia reynaudiana,POD enzyme was relatively higher under Pb and Cd stress in the early growth stage of Neyraudia reynaudiana,CAT enzyme activity was not significantly different under different heavy metal stress,indicating that CAT enzyme system started to participate in the REDOX system from the initial stage of heavy metal oxidative damage.Under the stress of Pb and Cr pollution,the peak activity of GR was one test cycle later than that of other oxidoreductases,and the GR oxidoreductase system could continue its metabolic activity at the late growth stage of high Pb pollution.However,under Cd pollution stress,there was a threshold of GR enzyme activity between 0.6mg/kg and0.8 mg/kg.This thesis has 36 figures,25 tables and 216 references. |
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