Study On Mechanisms For Phytoremediation Potential Of Copper Pollutions In Phragmites Australis-amf Symbiotic System

Currently, copper consumption in China has been ranked among the highest the world. The development of modern agriculture and industry, the great consumption and demand for copper, and the increase in mining and emissions in our country result in serious environment pollution. Copper has become one of the most polluted heavy metal elements in China. Heavy metal pollution is characterized by its difficulty in degradation, hence phytostablization, phytoextraction and bioaccumulation are the main removal methods. However, several factors, such as decreased plant growth and physiological activity by heavy metal stresses, relatively low biological availability of pollutants, and different concentrations of copper with specific issues limit the process and efficiency of metal translocation. Therefore, based on mycorrhizal technology, we systematically analyzed how the arbuscular mycorrhizal fungi（AMF） inoculation reinforces the resistance and uptake under copper stress, through the establishment of a Phragmites australis（common reed）-AMF symbiotic system. The conclusions obtained are useful for determining dominant mycorrhizal effects. This can provide newer technology to the applications of mycorrhizal technology in copper-polluted environment phytoremediation.After the reed-AMF symbiotic system was established, we investigated plant growth and development, physiological characteristics, and the rhizosphere soil properties and microbial metabolism. The accumulated germination（AS） of P. australis seeds were respectively increased by 20.9% and 26.95% after inoculation of Funelliformis mosseae and Rhizophagus irregularis, while the coefficient of the rate of germination（CRG） of P. australis seeds were respectively increased by 10.81% and 4.59%. In addition, both F. mosseae and R. irregularis promoted the growth and development of the seedlings, especially in the underground tissues. The root length（Ro L） was respectively increased by 90.59% and 51.3%, while the elongation rate of root（ERr） was respectively increased by 91.7% and 51.19%. Overall, both AMFs increased the usage efficiency of water, carboxylates and light. Moreover, the capability of P. australis to absorb P, S, B, Mg, K, Ca, Cu, Zn and Mo was improved by F. mosseae, and the capability of P. australis to absorb S, K, Ca, Cu and Zn was improved by R. irregularis.After invesgating the effects of AMF inoculation on the growth and development of P. australis under different concentrations of copper stress, we found that after the inoculation of F. mosseae and R. irregularis, the speed of germination was respectively increased by 27.1% and 22.8% when the concentration of copper was 5 mg l^-1. The growth and development of shoots and roots are inhibited by copper stress, and the inhibitory effect increases with the stress intensity. Copper concentrations of 1 mg l^-1 and 5 mg l^-1 are on the verge of the critical points of copper-induced damage on roots and shoots, respectively. Compared with shoots, the inhibitory effect of copper stress on roots was more prominent. When the concentration of copper was 1 mg l^-1 and 5 mg l^-1, the mycorrhizal dependency of R. irregularis-inoculated P. australis was 1.22 and 1.16, respectively, which was higher than the F. mosseae-inoculated ones, which had a mycorrhizal dependency of 1.09 and 1.05, respectively.After invesgating the effects of AMF inoculation on the physiological characteristics of P. australis under different concentrations of copper stress, we found that when the concentration of copper was 5 mg l^-1, the net photosynthetic rate were respectively increased by 53.83% and 75.26% after inoculation of F. mosseae and R. irregularis, while the transpiration rate and the stomatal conductance were not increased significantly. Under the same concentration of copper treatment both the shoots and roots of F. mosseae-inoculated and R. irregularis-inoculated P. australis had the nutrient elements’ concentrations with either an overall trend of decline or no significant changes compared to the control group. The changes in nutrients absorbed by AMF-inoculated P. australis were decreased when compared to control group. The contents of superoxide dismutase（SOD）, peroxidase（POD）, catalase（CAT）, ascorbate peroxidase（APX） and glutathione S-transferase（GST） in the roots of P. australis were relatively high compared with other related antioxidants. When the concentration of copper was 1 mg l^-1 and 5 mg l^-1, the SOD content were respectively increased by 26.25% and 42.3% after inoculation of F. mosseae, while the overall trend of R. irregularis- inoculated P. australis declined. Among all the Low-molecular-weight organic acids（LMWOAs） derived from the roots of P. australis, citric acid had the highest relative content. In addition, the total LMWOAs content increased with the concentration of copper stress, reached the maximum value when the concentration of copper was 1 mg l^-1, and then decreased. When the concentration of copper was 1 mg l^-1, the total LMWOAs levels were increased, while they decreased when the concentration of copper was 5 mg l^-1.After invesgating the effects of AMF inoculation on the copper absorption efficiency of P. australis under different concentrations of copper stress, we found that roots were more likely to accumulate copper. In addition, metal ions deposited near the cell walls firstly. Citrate-copper was the main chemical speciation of copper in P. australis. When the concentration of copper was 1 mg l^-1, the copper concentrations in shoots and roots of P. australis inoculated with R. irregularis were respectively increased by 80.03% and 33.6%, which were higher than F. mosseae-inoculated P. australis. The organs of P. australis were leaves, stems and roots by descending order according to citrate-copper content, with a proportional range of 36%-61%. Proteomic analysis results showed that under copper stress, a total of 459 proteins（200 up-regulated and 259 down-regulated） were identified as differentially expressed in P. australis roots due to inoculation of R. irregularis. Bioinformatics analysis showed that these differentially expressed proteins are mainly involved in respiratory electron transport chain, active transport of nutrient elements and the repair and degradation of abnormal proteins.AMF can alleviate the copper stress on reed growth, and intensify the resistance of reed. Promotion of the uptake and translocation of copper and the strengthening of reed is significant for the remediation of copper-polluted environments.