Ecological Effects Of Cd And Bensulfuron-methyl Combined Pollution On Soil Microorganisms

A series of laboratory incubation experiments were conducted to study the dynamic interaction effects of the combined pollution of cadmium and bensulfuron-methyl herbicide on the size of microbial biomass C (Cmic) and N (Nmic), soil basic respiration, N-mineralization (Nmin), soil phosphatase and sucrase activities with the time. The main results were summed up as follows:1. The results indicated that the soil Cmic and Nmic were decreased significantly as soil was treated with all levels of combined pollution of cadmium (2.5,10,50mg/kg) and bensulfuron-methyl herbicide(l,10mg/kg) within the initial 14 days, and then this inhibitory effect was decreased with the time. The interaction of cadmium and bensulfuron-methyl on the Cmic and Nmic was also significant. The microbial toxicity was found in the order of cadmium and bensulfuron-methyl>bensulfuron-methyl herbicide>cadmium. The interaction showed an synergistic effect of cadmium and bensulfuron-methyl combined pollution on Cmic was significant during the whole incubation period, however, there were two cases on Nmic. The interaction of the combined pollution on Nmic was synergistic when the cadmium concentration was higher (50 mg/kg), while it was antagonistic effect when the cadmium concentration was lower (2.5 and 10 mg/kg).2. The combined pollution of cadmium and bensulfuron-methyl resulted in an increase in the Cmic/Nmic ratio during the initial 28 days, and then no difference was found between all treatments and the control.3. The data showed that the combined pollution of cadmium and bensulfuron-methyl at different concentration levels decreased soil basic respiration and N mineralization during the initial incubation time, and then this toxic effect decreased with the time. The interaction effect of cadmium and bensulfuron-methyl was synergistic on soil basic respiration, especially during the initial 2856days. But no consistent results were observed about the interaction effect of cadmium and bensulfuron-methy on N mineralization at. different incubation time.4. All combined pollution treatments of cadmium and bensulfuron-methyl had significant effect on the soil phosphatase and sucrase activities as compared to the control, particularly during the initial incubation, and then declined with the time. Toxic effect on the activities of soil phosphatase and sucrase followed the order of cadmium and bensulfuron-methyl>bensulfuron-methyl herbicide>cadmium. The interaction of cadmium and bensulfuron-methyl on the activities of soil phosphatase and sucrase was synergistic.