| How to control soil pollution and reduce heavy metals mobility in the soil-plant system has become a focus of attention. Phytoremediation is a major development in recent years for cleaning up heavy metal pollution in green technology.The paper reviewed heavy metal pollution in the soil-plant system and outlined the effects of N on plant growth and the important role of plants to uptake heavy metals.Tall fescue were selected for pot experiments in the greenhouse and soil under the plantation of Chinese pine in Xishan Mountain of Beijing were selected for incubation experiments in the laboratory with orthogonal experiment design L16(45) to study the effects of N addition on physiological-biochemical properties, heavy metal uptake and soil enzyme activities in soil-turfgrass system under the soil compound pollution of Cd, Zn and Pb.The results showed that:(1) The biomass of tall fescue was inhibited by increasing N and Cd application. It increased at low concentrations of Zn and Pb but decreased at high concentrations. Chlorophyll content of tall fescue increased with increasing N application, while Zn had the opposite effect. There was no clear relationship between chlorophyll content and Cd application. Under certain heavy metal compound pollution, tall fescue showed a positive response of CAT activity at N and Cd application, but an inhibition response at Zn application. The total chlorophyll content, chlorophyll a and chlorophyll b content of tall fescue were significant positive correlated. There was significant negative correlation between fresh weight and chlorophyll a/b of tall fescue, which may indicate that the chlorophyll a/b, as a sign of leaf senescence, was closely related with the fresh weight of tall fescue. No significant correlations were found between CAT activity, fresh weight, total chlorophyll content, chlorophyll a, chlorophyll b content and chlorophyll a/b ratio. Variance analysis (ANOVA) showed no significant effects of N, Cd, Zn and Pb application on the biomass and CAT activity of tall fescue, while chlorophyll content was significantly affected.The application of N, Cd, Zn and Pb decreased soil pH. With the increase of N and Cd concentration, soil organic matter content increased. The application of Zn and Pb increased soil organic matter content at low concentrations, but had the opposite effect at high concentrations. The soil urease activity increased at N application, but.inhibited at Cd and Zn application. Lead promoted soil urease activity only at the concentration of less than 350 mg/kg. ANOVA showed no significant effect of N, Cd, Zn and Pb application on soil pH, organic matter content and soil urease activity in the pot experiment.(2) The uptake of Cd, Zn and Pb by tall fescue was dose-effect. Nitrogen stimulated the uptake of Cd and Zn at low concentrations (0 g/kg-0.5 g/kg). Once the concentration was up to 0.5 g/kg, the uptake of Cd and Zn was severely inhibited by N application. There would be an optimal concentration in promoting the uptake of heavy metals by tall fescue.(3) Soil samples with heavy metal compound pollution were incubated at 25℃for 40 days. Soil pH decreased with increasing Zn application, and with increasing incubation period as well. Soil urease activity had the overall declining trend with increasing Cd concentration, indicating that Cd inhibited soil urease activity. Soil urease activity increased first and then decreased at Zn application. In the first 30 incubation days, N, Cd, Zn and Pb application activated soil urease activity, but the activation effect gradually disappeared and showed an inhibitory effect afterwards. Cadmium had significant effects on soil acid phosphatase activity on the 10th,20th,30th and 40th day during incubation. Zinc and Pb had significant effects on soil acid phosphatase enzyme activity on the 20th and 30th day.Cadmium inhibited the soil alkaline phosphatase activity.(4) In the incubation process, with the increase of N, soil pH and urease activity increased, but soil acid phosphatase activity decreased. The effect of N on soil acid phosphatase activity was very significant, but soil alkaline phosphatase activity changed little when N was applied. There existed close correlation between soil pH and soil enzymes. Soil pH affected the enzymatic activity of both soil acid phosphatase and soil alkaline phosphatase.Nitrogen plays a certain role in controlling soil heavy metal pollution. There may be a suitable concentration at the interval of 0-0.5g/kg N application that can promote heavy metals uptake by tall fescue. Nitrogen application of more than 0.5g/kg could significantly inhibit heavy metals uptake. Meanwhile, Nitrogen has some effects on soil pH and soil enzyme activity under Cd, Zn and Pb compound pollution. |
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