| This paper was supported by the key project of national nuclear facilities decommissioning and radioactive waste management research (No.14ZG6101). The effects of uranium and its associated heavy metals on physiological and biochemical characteristics of pokeweed(Phytocacca Americana L.) were studied. The tolerance mechanism and detoxification mechanism of pokeweed for uranium and its associated heavy metals were analyzed. And the feasibility and application prospects of pokeweed to repaire uranium tailings were further discussed. The main results were as follows:(1) The germination rates of pokeweed were lower under single stress of uranium and its associated heavy metals (manganese, mercury, lead and arsenic) than that of the contrast, and the germination rates were 61.11%,58.00%,64.44%,75.55% and 62.22%, respectively.Under combining stress of uranium and its associated heavy metals, when the concentration of U was 37.5 mg/L, the concentration of Mn was 125 mg/L, the concentration of Hg was 1.25 mg/L, the concentration of Pb was 62.5 mg/L, and the concentration of As was 4 mg/L, the germination rate of pokeweed was 79.19% of the contrast. Uranium content was negatively related to the pokeweed germination rate (-6.388*). Mercury did not significantly impact the pokeweed seedling growth, while the effects of U, Mn, Pb and As on seedling growth were characterized by low-promoting and high-repressing. The maximum inhibition rates of U, Mn, Pb and As were 96.32%, 80.76%,88.40% and 70.40%, respectively. There was no significantly influence on the physiology-biochmistry indexes of seedling by low concentrations of uranium and associated heavy metals. While under high concentration of U, Mn, Pb and As, the soluble sugar content of seedling were reduced by 16.55%,16.61%,53.30% and 16.55%, respectively; the malondialdehyde content were increased to 2.67 times,1.61 times,1.19 times and 2.51 times, respectively. Compared with the contrast, the average activity of antioxidant enzymes were respectively reduced by 31.98%,58.38% and 28.11% under the stress of uranium, lead and arsenic; the average activity of antioxidant enzymes were increased by 48.11% under manganese stress.(2) The effects of uranium and its associated heavy metals (manganese, mercury, lead and arsenic) on the biomass of pokeweed were characterized by low-promoting and high-repressing. The threshold concentrations were 25 mg/kg,400 mg/kg,20 mg/kg, 200 mg/kg and 60 mg/kg, respectively. Under the highest concentration, the inhibition rates of biomass were 58.21%,16.88%,2.99%,32.71% and 51.68%, respectively. Under the complex stress, arsenic restrained the growth of pokeweed most significantly (R=-0.468); the interaction coefficient of uranium-manganese was-0.488; the interaction coefficient of uranium-lead was-0.301; the interaction coefficient of uranium-arsenic was-0.398. Under single stress of uranium and its associated heavy metals with high concentration, the soluble sugar contents was increased by 37.92%,16.96%,9.22%, 28.48% and 44.80% compared with the contrast,respectively; the superoxide dismutase (SOD) were increased to 1.94 times,1.15 times,1.19times,1.13 times,2.04 times of the contrast, respectively; the peroxidase (POD) were 90.70%,86.81%,82.98%,98.82% and 85.59% of the contrast, respectively; the catalase (CAT) were increased to 1.12 times,1.22 times,1.41 times,1.07 times and 1.33 times of the contrast, significantly; the content of malondialdehyde were increased by 39.01%,35.71%,39.83%,28.29% and 29.39% than that of the contrast, respectively. Under the stress of uranium, the content of chlorophyll a and chlorophyll b were decreased by 26.92% and 22.72% compared with the contrast, respectively. And the content of carotenoid was increased by 47.67%. Under the stress of manganese, the content of chlorophyll a, chlorophyll b and carotenoid were decreased by 27.74%,14.64% and 37.20%, respectively. Under the stress of mercury, the chlorophyll b content was decreased by 57.07% compared with the contrast and the changes of chlorophyll a and carotenoid contents were not significant. Under the sress of lead, the changes of chlorophyll a and chlorophyll b were not significant and the content of carotenoid was reduced by 25.58%, compared with the contrast. Under the stress of arsenic, the changes of chlorophyll a and coroteniod contents were not significant and the content of chlorophyll b was reduced by 11.61% compared with the contrast. Under the stress of uraium and its associated heavy metals (manganese, mercury, lead and arsenic), the net photosynthetic rates were decreased by 43.89%,28.45%,43.89%,24.09% and 40.51%, respectively.(3) When the content of uranium was 200 mg/kg in the soil, the accumulation of uranium in pokeweed was the largest. The content of uranium in root, stem and leaf were 133.57mg/kg,18.51 mg/kg and 22.41 mg/kg, respectively. The transfer coeffecient of pokeweed was 0.31. Under 50 mg/kg uranium stress, the maximum was 0.57. Under 800 mg/kg manganese stress, the accumulation of manganese in pokeweed was the largest. The manganese content in root, stem and leaf were 84.25 mg/kg,54.75 mg/kg and 519.50 mg/kg, respectively. The transfer coefficient was 6.81. When the content of mercury in soil was 40 mg/kg, the accumulation of mercury in pokeweed was the largest. The content of mercury in root, stem and leaf were 5.88 mg/kg,4.07 mg/kg and 5.16 mg/kg, respectively. The transfer coefficient was 1.92. Under 400 mg/kg lead stress, the accumulation of lead in pokeweed was the largest. The content of lead in root, stem and leaf were 47.10 mg/kg,28.20 mg/kg and 43.75 mg/kg, respectively. The transfer coefficient was 1.52. When the content of arsenic in soil was 120 mg/kg, the content of arsenic in root, steam and leaf were 2.05 mg/kg,0.13 mg/kg and 0.78 mg/kg, respectively. The transfer coefficient was 0.44. Under the combined stress of uranium and its associated heavy metals, there were antagonisms between uranium and manganese, mercury, arsenic. And there were synergy effects between uranium and arsenic, manganese and mercury, lead and arsenic. |
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