| This study used polycyclic aromatic hydrocarbons (PAHs, represented by naphthalene, phenanthrene, pyrene) and sulfur dioxide (SO2, used sulphate and sulfite as the main soil derivativatives) as the target pollutants. Freshly mixed loess born in Shanxi mining area was used as tested soil, while maize and alfalfa were chosen for tested plants. The experiments were conducted in the mini greenhouse, simulating condition required for soil culture. We applied biochemical and molecular biological techniques, such as PCR-DGGE and fluorescence quantitative PCR, etc. during the period of data collection.From the aspects of plant, we systematically studied the effects that PAHS-SO2alone and combinated pollution on maize and alfalfa germination rate, plant height, root elongation, biomass, alfalfa tissue antioxidant enzyme system (SOD, POD, CAT, GPX), soluble protein and malondialdehyde (MDA) contents; from the aspects of soil, pollution stress induced by PAHs and SO2was studied systematically in alfalfa soil enzyme activities (sucrase, urease, dehydrogenase) and the influence of soil microbial diversity. Meanwhile, this study tried to explore the relationship between the physiological changes and the plant tolerance induced by PAHs and SO2; The main results were as follows:(1) At low concentration, there were certain stimulative effects of PAHs-SO2under single and combined pollution on maize/alfalfa seed germination rate, but the impact was not significant. When concentrations of SO2(S4P0) and PAHs (S0P4) were increased, the seed germination rate of maize/alfalfa was significantly inhibited. In general, low concentration of PAHs-SO2promoted plant height and root elongation, the high concentration restrained above parameters in spite of the inhibitory effect on root length was more significant. The toxicity of single PAHs on alfalfas’ height was greater than that of SO2. Under the same concentration of PAHs-SO2, the inhibition on alfalfa root length was greater than that of maize. The combined effects of PAHs and SO2on alfalfa plant height and root elongation showed synergistic inhibition, but it showed antagonistic effect on plant height and root length of maize seedlings. In general, the influence of single PAHs or SO2and combined pollution on root biomass was greater than that of the aboveground biomass, the influence of PAHs was greater than that of SO2, the influence on alfalfa was greater than maize.(2) Protein content in leaf of alfalfa was increased at lower concentrations, while inhibited at higher concentrations under single pollution of PAHs or SO2. It was decreased significantly under combined pollution condition especially in case of SO2concentration more than10mg/kg. MDA content in leaf of alfalfa was the lowest in low concentration of PAHs (SOP1) or SO2(S1PO), and was the highest in high concentration of PAHs (SOP4) or SO2(S4P0). Under the combined pollution conditions, the oxidative damage of cell membrane was reduced at low concentration (SO2=10mg/kg); however, the joint actions of PAHs and SO2lead to the oxidative damage of cell membrane lipid when the concentration of SO2was up to10mg/kg, and MDA content was increased continuously.The effects on antioxidant enzymes activity influenced by SO2under the single pollution stress, compared with control. At low concentration of SO2, alfalfa leaf SOD and CAT activity were significantly induced, but GPX was suppressed when compared with the control. At high concentration of SO2, SOD enzyme activity was inhibited; SOD, CAT, GPX activity were significantly increased under the single pollution of PAHs. And under the single pollution of PAHs or SO2, POD activity was significantly inhibited when compared with the control. Under the combined pollution of PAHs or SO2, SOD and CAT activity were increased at low concentration, while at the high concentration the ability of induction was gradually decreased until to be inhibited; GPX activity was decreased at low concentration, while increased at high concentrations; POD activity was reduced at intermediate concentration, and was significantly inhibited at the the rest of the series of concentrations. (3) Under the single pollution of PAHs or SO2soil sucrase and dehydrogenase activities of alfalfa were decreased by low concentration (S1P0), were boosted by medium concentration (S2P0, S0P2), were suppressed by high concentration (S3P0～S4P0, S0P3-S0P4). Under the combined pollution of PAHs and SO2, at low concentrations (S1P1), sucrose enzyme activity was activated, dehydrogenase activity was showed synergistic inhibition, but no significant difference was found when compared with the control; at high concentration of PAHs and SO2(S3P3, S4P4), soil sucrase and dehydrogenase activities were all decreased and showed synergistic inhibition effect. Under the combined pollution of PAHs and SO2, soil urease activity was activated and higher than control. At low concentration (S1P1), soil urea enzyme activity was showed synergistic activation, but it was showed antagonistic activation at high concentration. By correlation analysis, soil invertase activity was showed a significant negative correlation with PAHs concentration; soil urease activity was showed a significant positive correlation with PAHs or SO2concentration.(4) The inhibitory impact of PAHs on alfalfa soil bacterial community diversity and microbial biomass was greater than the effect of SO2. At low and intermediate concentration SO2(S1P0～S3P0) or low concentrations of PAHs (S0P1～S0P2), soil bacteria species and microbial biomass were increased but bacterial community diversity was significantly inhibited at high concentrations of SO2(S4P0). Under single pollution of intermediate and high concentrations of PAHs (S0P3～S0P4), some soil microbial flora were disappeared. Under the combined pollution of PAHs and SO2, soil microbial diversity index was increased at low concentration (S1P1, S2P2), while it was significantly decreased at high concentration(S3P3, S4P4). |
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