Study On Stress Effects And Enrichment And Transport Characteristics Of Three Plants On Complex Heavy Metals

Tailings from mineral resources exploitation will cause a series of environmental problems such as soil heavy metal pollution.For tailings remediation,the traditional physical and chemical remediation methods are not difficult to cause secondary pollution to the environment,and in the process of remediation,the operation is difficult,and the cost is high.The above disadvantages can be prevented by using plants or microorganisms for bioremediation.In this study,plants combined with microorganisms were utilized to enrich heavy metals in tailings to reduce the harm of heavy metals to the environment through potting soil culture experiment.In order to investigate the enrichment effect of heavy metals in soil and the stress effect of heavy metals poisoning on three plants,alfalfa,ryegrass and maize,under different planting patterns.Potting soil culture experiment was conducted to simulate the conditions of composite heavy metals(Zn,Cd,Cr)pollution with five different concentration gradients.The three plants were planted under the three modes of single cropping,intercropping and intercropping with microbial agent.The plants were harvested after 45 days of growth.Chlorophyll,OJIP index,chlorophyll fluorescence parameters,two enzyme activities in rhizosphere soil and heavy metals content in plants were determined.The results showed that the three plants had different enrichment and transport effects on heavy metals under different planting conditions.The main results are as follows:(1)From the physiological indexes of plants,the physiological indexes of alfalfa were the best under the mono-cropping mode,while ryegrass and corn were better under the intercropping mode with fungi.The physiological indexes of alfalfa were promoted by low concentration and inhibited by high concentration under monocropping.The effects of different planting patterns on reducing soil p H were as follows: intercropping with bacteria <monoculture < intercropping.In the case of slight pollution in the intercropping mode,the soil p H can be effectively reduced,and the soil moisture content can be effectively improved.(2)From the perspective of plant photosynthesis,the performance of chlorophyll in alfalfa was mono-cropping > intercropping > intercropping with bacteria,ryegrass was intercropping with bacteria > intercropping > mono-cropping,and maize was intercropping with bacteria >intercropping > mono-cropping.The OJIP curve and chlorophyll fluorescence parameters of alfalfa showed the order of intercropping with bacteria > intercropping > mono-cropping under three planting modes.The OJIP curve and chlorophyll fluorescence parameters of ryegrass showed the order of mono-cropping > intercropping with bacteria > intercropping.The OJIP curve and chlorophyll fluorescence parameters of maize showed the order of mono-cropping >intercropping with bacteria > intercropping.The chlorophyll fluorescence parameters showed that the PSII reaction center would be damaged due to high concentration of complex heavy metals stress,and the damage degree was less under the intercropping and adding bacteria.(3)The POD activity of alfalfa under monoculture was the highest by comparing the two enzymes.Ryegrass and maize had the highest POD activity under intercropping with fungi,and CAT also showed the same trend.(4)From the enrichment of heavy metals in the three plants,the maximum Zn transport coefficient was 2.37 in alfalfa under intercropping and adding bacteria,the enrichment coefficient of Cd in ryegrass under intercropping and adding bacteria was greater than 1,and the enrichment coefficient of high concentration Cd in corn under intercropping was greater than 1.In conclusion,the content of heavy metals in aboveground and underground parts of the three plants increased with the increase of heavy metals concentration under the intercropping mode.In conclusion,combined with the analysis of hot spot map,it can be concluded that under the planting mode of intercropping and adding bacteria,the three plants have the best effect on the enrichment and transport of heavy metals,and the biochemical indexes of various plant growth indicators,chlorophyll content,photosynthetic structure and enzyme activity have the best tolerance to heavy metals.At the same time,soil moisture content and p H can be effectively improved.