Effects And Mechanisms Of Exogenous Nitric Oxide And Metal-Chelators Assisted Phytoremediation Of Cadmium-Contaminated Soil Using Ryegrass(Lolium Perenne L.)

With the development of industry and the rapid expansion of cities,heavy metal pollution in soil has become increasingly serious,among which cadmium has been identified as a priority heavy metal because of its high content in soil and its threat to human health.Cadmium is easily absorbed and accumulated by plants,leading to crop loss and harm to human health.This test by ryegrass（Lolium perenne L.）as materials,using pot with liquid culture test,the method of the combination of nitric oxide（NO）is studied respectively with ethylenediaminetetraacetic acid（EDTA）,ethylenediamine succinic acid（EDDS）and citric acid（CA）joint strengthening ryegrass effect and the mechanism of resistance to cadmium and the cadmium absorption,and screen the optimal adding chelating agent concentration.The main research results are as follows:1.In the pot experiment,50mg kg^-1Cd had obvious inhibitory effect on the growth of ryegrass,and 25mg kg^-1 Cd had obvious inhibitory effect on the growth of ryegrass,and its inhibitory degree increased with the increase of the number of stubbles cutting.Adding SNP and low concentration(2mmol kg^-1)EDTA can alleviate Cd stress of ryegrass,improve its root activity and antioxidant enzyme activity,and reduce malondialdehyde content and electrolyte leakage.Exogenous addition of SNP and EDTA can effectively improve soil enzyme activity.At the same time,the addition of EDTA at different concentrations can significantly improve the contents of available and potentially available cadmium in the soil,so as to significantly improve the Cd absorption of ryegrass and the cadmium accumulation in the above ground,among which the extraction efficiency of adding SNP and 2mmol kg^-1EDTA and the cadmium accumulation in the above ground are the highest.In this experiment,the addition of 100m L 300μmol L^-1 SNP and 2mmol kg^-1 EDTA not only effectively alleviated the stress of cadmium on the growth of ryegrass,but also significantly increased the accumulation of cadmium in ryegrass,with the highest extraction efficiency and the best effect.And the total extraction and accumulation of cadmium in ryegrass could be effectively increased by multiple cutting.Under the condition of liquid culture,the exogenous EDTA and SNP significantly reduced the plant height,root length and root activity of ryegrass under the non-cadmium stress,and significantly increased the O₂^·-production rate,H₂O₂ and MDA contents in the above and underground parts of ryegrass.100μmol L^-1 Cd severely inhibited the growth of ryegrass.Adding SNP and EDTA can alleviate the damage of cadmium stress to ryegrass.At the same time,the cadmium content in both above ground and underground parts increased significantly.Under cadmium stress,exogenous addition of SNP and EDTA can promote cadmium absorption in ryegrass,improve the accumulation of cadmium in the above ground and enhance its cadmium resistance at the same time,and effectively alleviate the inhibitory effect of cadmium stress on the growth of ryegrass.In this study,adding 0.25μmol L^-1 EDTA and 50μmol L^-1 SNP at the same time had the best effect on improving the resistance to Cd stress and Cd accumulation of ryegrass.2.In the pot experiment,compared with CK,the addition of 50mg kg^-1 Cd significantly inhibited the growth of ryegrass.Under cadmium stress,adding SNP and low concentration(2.5mmol kg^-1)EDDS could alleviate the growth inhibition of ryegrass,improve its root activity and antioxidant enzyme activity,and reduce malondialdehyde content and electrolyte exhalation rate.At the same time,the addition of EDDS at different concentrations can significantly improve the effective state content in the soil,so as to significantly improve the Cd enrichment coefficient of ryegrass and the above-ground cadmium content.Among them,the extraction efficiency of SNP and 2.5mmol kg^-1 EDDS and the above-ground cadmium accumulation are the highest.In this experiment,the addition of 100m L 300μmol L^-1 SNP and 2.5mmol kg^-1 EDDS not only effectively alleviated the stress of cadmium on the growth of ryegrass,but also significantly increased the accumulation of cadmium in ryegrass,with the highest extraction efficiency and the best effect.Under the condition of liquid culture,100μmol L^-1 Cd seriously inhibited the growth of ryegrass.Adding SNP and EDDS can alleviate the damage of cadmium stress to ryegrass.Under the cadmium stress,exogenous addition of SNP and EDDS can promote the cadmium absorption of ryegrass,improve the accumulation of cadmium in the above ground and enhance its cadmium resistance at the same time,and effectively alleviate the inhibitory effect of cadmium stress on the growth of ryegrass.In this study,the addition of SNP alone under cadmium stress had the best mitigation effect,but the addition of 0.25mmol L^-1 EDDS and 50μmol L^-1 SNP at the same time could significantly increase the Cd accumulation of ryegrass while improving cadmium resistance,and the comprehensive effect was the best.3.In the pot experiment,under cadmium stress,adding SNP and 1 and 5mmol kg^-1 CA could alleviate the growth inhibition of ryegrass,improve its root activity and antioxidant enzyme activity,and reduce malondialdehyde content and electrolyte exhalation rate.The activity of soil urease,catalase and sucrase could be improved effectively.At the same time,adding CA at different concentrations can significantly improve the content of available states in the soil,thus significantly improving the Cd enrichment coefficient of ryegrass and the above-ground cadmium content,among which the extraction efficiency of adding SNP and5mmol kg^-1 CA and the aboveground cadmium accumulation are the highest.In this experiment,the addition of 100mL 300μmol L^-1 SNP and 5mmol kg^-1 CA had the strongest mitigation effect on cadmium stress of ryegrass.Meanwhile,the cadmium accumulation and extraction efficiency of ryegrass were the highest under this treatment,and the enhanced repair effect was the best.Under the condition of liquid culture,the growth inhibition of ryegrass under cadmium stress could be alleviated by adding SNP and CA alone and in combination.Under cadmium stress,exogenous addition of SNP and CA can promote cadmium absorption in ryegrass,improve the accumulation of cadmium in the aboveground and enhance its cadmium resistance at the same time,and effectively alleviate the inhibitory effect of cadmium stress on the growth of ryegrass.In this study,the addition of 2.5mmol L^-1 CA and 50μmol L^-1 SNP at the same time under cadmium stress had the best mitigation effect on cadmium stress in ryegrass,and significantly increased the accumulation of Cd in ryegrass.