Uptake And Enrichment Of Cu And Zn In Hydroponic Ryegrass Enhanced By LED3A

Cu and Zn are common targets in the field of environmental remediation of heavy metal pollution.They are adjacent sub-group elements of the same cycle,with certain similarities in properties,and both are essential elements for plant and animal growth,and are often found together in fishery and livestock production wastewater.It is of research significance to explore methods of treatment for Cu and Zn pollution.Phytoremediation technology has good potential in the remediation of heavy metal polluted environments due to its green and economic characteristics,but is limited to its disadvantages such as long lead time and low efficiency,and is subject to many restrictions in its practical application.To improve the efficiency of phytoremediation,it is often supplemented by other technical means to carry out combined remediation treatment,of which chelation-induced enhancement is a typical combined chemical-phytoremediation technology,which can improve the absorption and extraction efficiency of heavy metals by plants to achieve good remediation effect,and has become one of the hot spots of heavy metal pollution treatment research.EDTA is often used in chelation-induced phytoremediation because of its strong chelating ability for a variety of heavy metals,but EDTA has certain biological toxicity and is difficult to be biodegraded,which can easily produce secondary pollution to the environment.Therefore,N-dodecanoyl ethylenediamine triacetate（LED3A）was chosen as the fortifying reagent in this study.LED3A is a derivative of EDTA with good chelating properties and is readily biodegradable,which can be used to enhance the remediation of heavy metal contamination by plants and reduce the risk of secondary contamination.In this study,LED3A was used in combination with ryegrass in a hydroponic experiment to investigate the growth status,physiological response and Cu and Zn uptake enrichment of ryegrass plants under single and combined Cu and Zn stresses by LED3A reinforcement.The biomass,photosynthetic levels,antioxidant enzyme activities（peroxidase POD,superoxide dismutase SOD and catalase CAT）,degree of membrane lipid peroxidation（malondialdehyde MDA,superoxide anion O₂^-and hydrogen peroxide H₂O₂）,as well as the accumulation of Cu and Zn and their subcellular distribution in the plant were examined to analyse the effects and patterns of Cu and Zn uptake and extraction by LED3A-enhanced ryegrass.The main findings of the study are as follows:（1）The biomass of ryegrass seedlings under single and combined stresses of Cu and Zn increased and then decreased with increasing LED3A concentrations.50 mg/L of LED3A showed the best efficiency of enhanced extraction from ryegrass seedlings.Extraction increased with time of fortification,reaching a maximum at 288 h.The extraction of Cu and Zn by ryegrass was 1.34 and 1.29 mg under single stress and 1.36 and 1.05 mg under combined stress,respectively.（2）Suitable concentrations of LED3A increased the biomass of ryegrass compared to the unenhanced treatment,with inhibition occurring above 100 mg/L.The overall photosynthetic pigment content decreased more significantly when the LED3A concentration was increased to 200 mg/L,indicating that high concentrations of LED3A had an effect on the photosynthetic levels of ryegrass.（3）LED3A significantly increased the activity of antioxidant enzymes（POD,SOD and CAT）in ryegrass,thereby enhancing the scavenging of reactive oxygen species（e.g.O₂^-and H₂O₂）.The appropriate concentration of LED3A will reduce the MDA content in ryegrass and alleviate the membrane lipid peroxidation damage caused by Cu and Zn stress,while 200mg/L LED3A will cause an increase in MDA content and intensify the toxic effects of stress.（4）The subcellular distribution of Cu and Zn in ryegrass is more predominant in the cell wall of the belowground part and more in the cytoplasm of the aboveground part.The mechanisms of resistance to Cu and Zn in the lower and upper parts of ryegrass when LED3A coexists with heavy metals are fixed precipitation by the cell wall and compartmentalisation by the vesicles,respectively.The optimum LED3A fortification concentrations were 50 and100 mg/L for copper and zinc single stresses,respectively,with corresponding extraction and fortification efficiencies of 76.16%and 74.53%and 38.13%and 38.24%,respectively.The optimum fortification concentration under combined stress was 50 mg/L,with extraction and fortification efficiencies of 77.42%and 61.26%and 32.18%and 26.44%for Cu and Zn,respectively.