| Polycyclic Aromatic Hydrocarbons (PAHs) and heavy metals are two typical environmental persistent pollutants, which are often occurred simultaneously in soil. They migrate along the food chain, transfer or enrich, and have the potential hazards to human health. Thus remediation PAHs and heavy metals contamination soil has become one of the hot issues in domestic and international scientifical research. In this paper, taking two kind of raw mixed-loess soils (chestnut soil and cinnamon soil) collected form Antaibao and Taigu industrial and mining areas in Shanxi as tested soil, and ryegrass (Lolium perenne L.) as test plant material, through greenhouse pot experiments, using biochemical techniques and denaturing gradient gel electrophoresis techniques (PCR-DGGE), the ecological adaptability of ryegrass on single and combined PAHs and mercury (HgCl2) contaminated soils was studied. The key topics focused on PAHs and HgCl2 single or combined contaminated soils on seed germination of ryegrass, plant cytochrome P450 enzymes and antioxidant enzyme systems, and their impacts on soil enzyme activities and microbial community diversity, the main research results are as the follows:(1) Ryegrass germination rate is more sensitive to HgCl2 pollutants,In PAHs-HgCl2 single or composite pollution treatment, the results showed that low and medium concentrations of ryegrass seed germination rate play a stiulation role, while high concentrations were inhibited. The synergistic effects of medium concentration of PAHs-HgCl2 combined treatment on ryegrass seed germination were showed, while the inhibition effects of high concentrations of PAHs-HgCl2 combined treatment on ryegrass seed germination were showed.(2) 180 d after ryegrass planting, cytochrome P450 enzyme content of ryegrass is more sensitive to PAHs pollutant than that in HgCl2, and under different concentrations of PAHs treatments, the cytochrome P450 enzyme of ryegrass leaves levels are both higher than that of in the control group. In the PAHs-HgCl2 single or combined pollution treatments, with the increase of concentrations of pollutants, cytochrome P450 enzyme content generally increased at the first and then decreased. When concentration of PAHs arrivaled 10 mgkg-1, it might maybe the threshold value of P450 enzyme, and P450 enzyme levels decreased when the concentration of PAHs exceeded 10 mgkg-1.(3) In the PAHs-HgCl2 single or combined pollution treatments,180 d after ryegrass planting, SOD and POD activities of ryegrass leaves increased first and then decreased. When concentration of HgCl2 arrived at 10 mg · kg-1, SOD activity of ryegrass leaves increased greatly and reached the peak with significant difference (P<0.05); In the PAHs-HgCl2 single or combined pollution treatment, with increasing concentrations of pollutants, MDA levels of ryegrass continued to increase and MDA content of ryegrass leaves showed a significant positive correlation.(4) In the PAHs-HgCl2 single or combined pollution treatments,180 d after ryegrass planting, with increasing concentrations of PAHs-HgCl2, soil catalase activity increased first and decreased after an initial increase while soil urease activity and concentration showed a significant positive correlation with concentrations of PAHs-HgCl2; soil catalase contamination is more sensitive to PAHs compared to HgCl2, when concentrations of PAHs greater than 100 mgkg-1, catalase activity was significantly inhibited. Soil urease activity of combined PAHs-HgCl2 treatments showed synergistic inhibition.(5) Different contaminated soil had many common bands, and this indicated ryegrass growth soil environment was suitable for the survival of certain soil microorganisms. Low and medium concentrations of pollutants treatments showed induced effects on soil microorganisms which caused soil microbial community diversity showed an increasing tendency, while the high concentrations of PAHs or HgCl2 produced inhibition effects resulting in the number of microbial population decrease, which caused soil microbial community diversity showed a decreasing tendency. Microbial diversity reached the highest value of soil microbial community diversity at the medium concentrations of pollutants treatment of A22 (P3H3), accompanied by a number of new bands, and showed synergistic effects on soil microorganisms.The research results showed that:under the two types of raw mixed-loess soils (chestnut soil and cinnamon soil) collected form Antaibao and Taigu growing conditions, influence of PAHs-HgCl2 pollutants on ryegrass seed germination, plant cytochrome P450 enzyme activities, antioxidant enzyme activities and soil enzyme activities, and soil microbial community diversity had the similar rules. But the relevant data of ryegrass growth in Taigu raw mixed-loess soils were slightly higher than that in the loess Antaibao raw mixed-loess soils, which showed that ryegrass growth in Taigu raw mixed-loess soils were more sensitive, that is, showed the stimulation and inhibition effects. The results indicated that ryegrass has more significant ecological adaptability and remediation effects on the contaminated soil of Taigu. |
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