Compound Exposure Of Polycyclic Aromatic Hydrocarbons And Cadmium In Soil And Its Biological Effects On Ryegrass

With the development of science and technology in China,now we enjoy the dividends brought by the industrial revolution.However,the trend of industrialization has also led to various damage to the environment in which we live.Since the"13th Five-Year Plan"period,we have achieved positive results in environmental pollution prevention and control,but environmental pollution problems in some areas are still prominent,especially the problem of soil pollution,which threatens the ecological environment and human health.The complexity of the soil environment has led to new problems and severe challenges in soil pollution control in China.In this study,the typical heavy metal pollutant cadmium（Cd）and organic pollutants polycyclic aromatic hydrocarbons（PAHs）in soil were used as the research objects,and ryegrass（Lolium perenne L.）was used as the test plant,and the biological effects of soil Cd and PAHs on ryegrass were investigated.The soil culture experiment was used to simulate poisoning of the soil.Ryegrass was cultivated using mock-poisoned soil and field soil.The changes of ryegrass antioxidant enzyme activities and the concentration of oxidative stress products were analyzed.A dose-response relationship was established to study the changes of the physiological mechanism of ryegrass under compound pollution stress.At the same time,the metabolomics,transcriptomics and proteomics of ryegrass were measured to study the impact of Cd and PAHs compound pollution on the biological effects of ryegrass,which also provided a scientific basis for the ecological risk assessment of site pollution.The main results are as follows:（1）Twelve typical oxidative stress indicators of ryegrass include superoxide dismutase（SOD）,peroxidase（POD）,catalase（CAT）,nitrate reductase（NR）,glutathione reductase（GR）,polyphenol oxidase（PPO）,phosphoenolpyruvate carboxylase（PEPC）,malondialdehyde（MDA）,hydrogen peroxide（H₂O₂）,cysteine（Cys）,proline（Pro）and reduced glutathione（GSH）were determined in response to single or combined exposure of Cd and PAHs.The results showed that the four indicators of PPO,PEPC,GSH,and Pro had common changes under pollutant stress.At the same time,the indicators of ryegrass in the background soil and field soil were measured,and the change trends of the four indicators of Pro,NR,MDA,and CAT were found.It has something in common with the results of artificially spiked soil and can be used as an indicator to identify actual site pollution.（2）Since the four indicators of PPO,PEPC,GSH,and Pro have the characteristics of common changes,we explored the dose-response relationship.It was found that under single Cd exposure,the PPO enzyme activity of ryegrass showed a downward trend,the PEPC enzyme activity and Pro concentration both increased first and then decreased,and the GSH concentration showed an upward trend.Under single PAHs exposure,the PPO enzyme activity of ryegrass showed a downward trend,and the activity of PEPC and the concentrations of Pro and GSH increased first and then decreased.At the same time,we found that compared with single Cd exposure,under the combined exposure of Cd-PAHs,the change trends of the four indicators of ryegrass had evident changes.The significant down-regulation of the activities of PEPC and PPO enzymes and the concentrations of Pro and GSH may be important indicators of the combined pollution of high concentrations of PAHs and Cd in the soil of the site.Moreover,under compound exposure stress,the four indicators of ryegrass generally showed antagonistic effects.（3）Multi-omics analyses were used to analyze the metabolomics,transcriptomics,and proteomics of ryegrass under single or compound stress of Cd and PAHs.It was found that compared with the blank group,the exposure group in the three omics had changes in the corresponding metabolites,genes,and proteins,and the corresponding functions and changes in the metabolic pathways were enriched.These substances and pathways can reflect the response mechanism of plants when they are under stress by exposure to Cd and PAHs.At the same time,the joint pathway analysis of metabolomics and transcriptomics and proteomics was carried out respectively,and it was found that there were 4 metabolic pathways enriched in the joint analysis of metabolomics and transcriptomics with significant changes.There was a significant change in one pathway in the joint analysis of metabolomics and proteomics,and this pathway was also expressed in the joint analysis of metabolomics and transcriptomics.In this study,it was observed that the compound pollution of heavy metal Cd and PAHs had a dose-response relationship on typical plant oxidative stress indicators,and also affected the expression of some plant genes,proteins,and metabolites,and these substances can be used as indicators for site compound pollution.The ecological risk assessment provides theoretical support.