| For the past few years,with the fast development of intensive animal husbandry, the annual consumption of livestock feces containing veterinary antibiotics and heavy metals has been gradually increased. However, a large number of antibiotics and heavy metals into soil environment would lead to the phenomenon of compound pollution in soil, which is harmful to soil ecosystem and human health. To evaluate the potential influence of antibiotics and heavy metals on soil ecosystem, the study of single and combined pollution of three kinds of antibiotics oxytetracycline(OTC),enrofloxacin(ENR),sulfadimidine(SM2)(0, 0.05, 0.20, 0.80 mmol/kg) and Cu(0, 1.60 mmol/kg) at a ratio of 1:2, 1:8, 1:32 on 7, 14, 21, 28 d, using enzyme activity photometry method and Biolog ECO-plate, was carried out under the condition of indoor simulation. The results could be summarized as follows:1. Single and composite toxicity of OTC, ENR, SM2(0, 0.05, 0.20, 0.80 mmol/kg) and Cu(0, 1.60 mmol/kg) on soil enzyme activity:(1) As to single pollution, heavy metal Cu at the concentration of 1.60 mmol/kg has certain inhibitory effect on the four kinds of soil enzyme activity, but the inhibitory degree among them is different and the inhibition ratio was urease > invertase > acid phosphatase > catalase.Under the single processing of OTC, it inhibit the activity of invertase, and this effect got stronger along with the higher concentration; the high concentration treatment(0.80 mmol/kg) showed significant inhibitory effect on the activity of urease and phosphatase; there is no obvious difference in catalase activity between each OTC treatment and control group. Under the treatment of low concentration ENR, sucrose enzyme activity showed the trend of "activated- inhibition- activated ", the sucrose enzyme activity was inhibited under the high concentration ENR; acid phosphatase activity was activated under all ENR single treatment, as the extension of incubation time, activation function was abated; as to the activity of urease, compared with control, low concentration ENR showed early inhibitive effect, slightly late activation; the all single ENR treatments showed mild activated effect on activity of catalase. As to the single pollution of SM2, the activity of invertase is much lower than it of control group; Low concentration SM2 showed activated effect on acid phosphatase, high concentration SM2 has a significantly inhibitory effect on acid phosphatase activity; High concentration treatment has a significantly inhibitory effect on urease activity; as to hydrogen peroxide enzyme, low concentrations(0.05, 0.20 mmol/kg) showed the significantly activated effect on 7th and 21 th day.Compared with control group, the activity of hydrogen peroxide enzyme under high concentration(0.80 mmol/kg) has no significant difference.(2) As to combined pollution, the combined pollution of OTC and Cu inhibit the activity of sucrase, and the higher the concentration of OTC was, the stronger the inhibition effect was. The combined pollution of OTC and Cu has a significantly inhibitory effect on the activity of the acid phosphatase and the urease. At the early stage, the combined pollution of the low concentration(0.05, 0.20 mmol/kg) OTC and Cu has an significantly promoting effect on hydrogen peroxide enzyme, and the effect disappear in the late period. About the case of the combined pollution of ENR and Cu, compared with control group, the activity of invertase and acid phosphatase, urease were significantly suppressed. However, it had little impact on the activity of hydrogen peroxide enzyme. Under the composite pollution of SM2 and Cu, invertase and acid phosphatase, urease activity were significantly suppressed, the hydrogen peroxide enzyme inhibition was promoted at the early stage and inhibited in the late period. As to the type of interaction, from the entire test period, interaction type of joint toxicity effects of ENR and Cu on soil enzymes in infected 7 and 28 days is mainly synergistic effect and the interaction type on the 14 th and 21 th day is opposite, OTC composite treatment in the whole experimental period is mainly antagonism effect, however, as to composite treatment of SM2 and Cu, owing to the influence of concentration and processing time, it displayed more complex antagonism and collaborative interaction types, the composite treatment group of the high concentration SM2(0.8 mmol/ kg) and Cu at the early stage displayed antagonism effect, and mainly displayed are mainly synergistic effect in the late stage.2. Effects of single and compound pollution of three kinds of antibiotics and Cu on the functional diversity of soil microbial community(1)Under the single pollution, AWCD value was significantly decreased under the Cu with a concentration of 1.60 mmol/kg, whole microbial activity was inhibited, there were no significant influence on Shannon index but the Simpson index showed a significant inhibitory effect. The single treatment group of OTC and ENR reduced the AWCD value, the Shannon, Simpson index showed some inhibitory effect, and showed that the microbial abundance and evenness were decreased. The SM2 value has little influence on the AWCD, SM2 single treatments under the Shannon index were not significantly different with the control, the main performance of the Simpson index was inhibited. On the whole, the inhibitory effect of the three antibiotics on the overall microbial activity was OTC>ENR>SM2, it also verified the change of functional diversity index under the treatment of three antibiotics and Cu.(2) Compound pollution, ENR and Cu compound treatment, In addition to the high concentration of ENR(0.8M) and Cu composite group of AWCD was promoted, Other processing is mainly showed reduced. There was no obvious influence on the Shannon index and the difference compared with the control was not significant. The Simpson index showed a certain promotion effect on the 14 th day and showing an inhibitory effect at the low concentration after 21 days, and the high concentration compound showed a slight activation. The AWCD were significantly decreased under the OTC and Cu combined treatment group, the Shannon index is lower than that of the control and in the state of being suppressed, the Simpson index compared with that of the control was significantly inhibited. The combined treatments of SM2 and Cu had little effect on the AWCD, the Shannon index had no significant difference compared with that of the control, and it showed obvious inhibitory effect on the 14 th day, but showed no significant difference after 21 days.3. From the research results of the analysis of difference of toxicity, we can safely draw the conclusion that the factors including types of antibiotics, concentration, infected time, types of enzyme, have an influence on its toxicity on soil enzyme activity. Interaction types of compound pollution were not simple addition of single function toxicity, but involved closely with the incubation time and the types of antibiotics, and because of the factors above, the interaction type will show antagonism effect and synergy effect. |
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