Analysis of Soil Microbial Flora Based on Carbon Source Utilization Pattern and Assessment of Pesticides Effects on Rice Paddy Soil Ecosystem.

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The Biolog method was examined as an isolation-independent method to characterize microbial flora by incubating total microbial inoculum from paddy soil samples. Then, the natural fluctuation in the soil microbial population, biomass, activity and flora of two different rice paddies (low-chemical-input and conventional) were monitored during two growing seasons as reference in order to assess the side-effect of pesticides on soil ecosystem. Effect of two pesticides on soil microbial flora was also examined using the Biolog method in laboratory experiments.1) Evaluation of the Biolog method to characterize microbial floraThe Biolog GN plate was inoculated with diluted soil solutions and absorbance values at each well were measured periodically. Patterns of the positive wells in the Biolog plates could be grouped by the cluster analysis using the SPSS software.2) Natural variability in soil microbial population, biomass, activity and floraThe coefficient of variation for each parameter w … More as as follows : nitrification activity (16-20%), ammonification activity (39-53%), protease activity (31-62%), ammonium oxidizer (88-174%), microbial biomass nitrogen (19-37%), microbial biomass carbon (15-30%), ATP content (28-44%), aerobic bacteria (39-46%), Gram-negative bacteria (51-59%), anaerobic bacteria (42-61%), and fungi (33-52%). There was no significant difference in the values between the two paddies.Microbial flora in both paddies was separated into two major groups, which belonged to flooded and unflooded periods, indicating that the characteristic microbial flora was formed in the oxidative and reductive soil environments.These results indicate that the microbial parameters measured in this study fluctuate by natural stresses as well as anthropologic stresses. Therefore, these results should be used as reference when conduct risk assessment of pesticides to the microbial rice paddy soil ecosystem.3) Effect of pesticides on soil microbial floraDifferent microbial flora caused by soil flooding and application of pesticide was detected using the Biolog method. Effect of the pesticides on microbial flora could be assessed by comparing it with the effect of changes in the soil redox conditions, which have the most significant effect on microbial flora in paddy soils. Less