Physiological Response Of Rhizobium-alfalfa Symbiosis In Copper Stress And Its Remediation Effect In Polluted Soil

With the development of modern industry and human activities,the problem of heavy metal pollution is serious,and soil heavy metal pollution has become the focus of environment protection problems.Microbial phytoremediation has gotten great concern due to green and economic advantages.Through pot experiment,the study which was used copper as the heavy metal pollutant,rhizobium-alfalfa symbiosis as the research object analyzed the physiological response of alfalfa to copper under inoculating rhizobium and the overall effect of rhizobium-alfalfa symbiosis on repair copper contaminated soil.The main progress and results as follows:?1?With the increasing of copper concentration,alfalfa growth was inhibited,but inoculating rhizobium could significantly reduced copper stress.The highest resistance copper concentration of alfalfa increased from 200 mg·kg^-1 to 400 mg·kg^-1.The rhizobium-alfalfa symbiosis could improve the growth of alfalfa chlorophyll synthesis,photosynthetic reaction and the total nitrogen content.?2?Under copper stress of 300 mg·kg^-1,the shoot and root copper content of the control were 31.78±1.71 mg·kg^-1 and 41.07±3.47 mg·kg^-1,respectively,which were the highest in control treatment,but the shoot and root copper content of the inoculation treatment in 300 mg·kg^-1 of copper stress were 65.7%and 158.8%higher than that of the control.However the highest shoot and root copper content of the inoculation treatment were in 400 mg·kg^-1 of copper,which were 33.02±4.84mg·kg^-1and 124.44±24.06 mg·kg^-1 respectively.They were 1.31 times and 2.72times of the control in 400 mg·kg^-1.In 100 mg·kg^-1 copper stress,the alfalfa shoot and root uptake content of the inoculation treatment were 6.1%and 79.5%more than the control.In 200 mg·kg^-1 copper stress,the alfalfa shoot and root uptake content of the inoculation treatment were 2.53?g per plant and 16.78?g per plant more than that of the control.?3?With the increasing of Cu stress,MDA,O₂^-and H₂O₂ content of shoot and root were increasing gradually,inoculating rhizobium inhibited the generation of harmful products.Inoculating stimulated antioxidant enzyme system,enhanced the activities of SOD,POD,CAT and APX,promoted the enzymatic reaction to consume oxygen free radical,improved the balance of plant cell,released the stress.Rhizobium-alfalfa symbiosis is helpful to produce materials such as GSH,which stimulate the system of AsA-GSH,regulate the redox electricity of AsA/DHA and GSH/GSSG to control the redox balance,at last to achieve the aim of improve the resistance of plants.?4?Rhizobium had no significant difference to the distribution of soil copper forms,but had obvious effect on soil copper removal rate.Inoculation treatment could make the soil copper removal rate increased from 7.1%to 10.8%.Inoculation had no significant effect on soil pH,while remarkably increased SOM and TN which increased by 7.8%and 6.8%,respectively.?5?Compared with the control,the biomass of shoot and root with inoculation increased by 57.9%and 33.3%,respectively under copper polluted soil.And chlorophyll content increased 0.22 mg·g^-1,photosynthetic rate increased by 13.2%,TN of root increased by 11.6%while TN of shoot had no significant alteration.?6?Inoculation treatment increased the copper content and uptake content of shoot and root under copper polluted soil.Compared with the control,the copper uptake content of shoot and root with inoculation increased by 104.0%and 41.0%,respectively,and the total accumulation increased from 628.94±38.05?g per pot to990.11±42.41?g per pot.The transfer ability and accumulation ability had no difference.?7?Compared with the control,SOD,POD,CAT and APX of alfalfa shoot increased by 42.2%,33.9%,63.0%and 14.3%,respectively under rhizobium-alfalfa symbiosis.Those of alfalfa root increased by 80.7%,52.8%,24.0%and 69.8%.Inoculation treatment reduced MDA content of shoot and root,which reduced by27.7%and 36.1%,respectively.Under inoculation treatment,O₂^-content of shoot and root were 2.6%and 12.0%lower than those of the control.However,H₂O₂ content of shoot was 20.0%higher than that of the control,H2O2 content of root had no difference.