Effects Of Myclobutanil On Soil Microbial Activities, Populations And Soil Nitrogen Transformations

Myclobutanil is an efficient triazole fungicides, which is mainly used to control the plant diseases caused by ascomycetes, basidiomycetes and deuteromycetes and often used in wheat field. Myclobutanil has a long half-life in field and it may pose a potent ial threat to the soil microbes and soil nitrogen transformations after the sustained and extensive application. A 3-month-long experiment was carried out to ascertain the effects of different concentrations of myclobutanil(0.4 mg kg-1, T1; 1.2 mg kg-1, T3; and 4 mg kg-1, T10) on soil microbial activities, populations and soil nitrogen transformations using two typical wheat field soils(Henan fluvo-aquic soil and Shanxi cinnamon soil) in China. Throughout the cultivation experiment, soil was sampled after 7, 15, 30, 60, and 90 days of incubation and determined using the microbiological indicators of system of soil environmental safety assemssment combined with the real-time quantitative PCR. The main findings are as follows:1. In this work, the determination of myclobutanil residues in soils was conducted by the combined use of modified quick, easy, cheap, effective, rugged, and safe(Qu ECh ERS) extraction procedure and ultra-performance chromatography/tandem mass spectrometry(UPLC–MS/MS). The method showed excellent linearity(r=0.999) in the range of 0.01~0.5 mg L-1. The mean recoveries from soil matrices spiked at 0.2,4 mg kg-1 were ranged from 80.1% to 113.0% with the intra-day relative standard deviations(RSD) in the range of 4.48~7.79%. The degradation dynamics of different concentrations of myclobutanil in Henan Fluvo-aquic soil and Shanxi cinnamon soil were all met the first-order kinetic equation. The half-lives of the different concentrations varied from 20.3 to 69.3 days in Henan F luvo-aquic soil and from 99 to 138.6 days in Shanxi cinnamon soil. The degradation characteristics of myclobutanil in Henan Fluvo-aquic soil was moderately, but in Shanxi cinnamon soil, it was comparatively difficult.2. The application of high concentration myclobutanil(4 mg kg-1) significantly inhibited the soil microbial basal respiration, soil microbial biomass C, the gene abundance of total fungi and bacteria in Henan Fluvo-agvic soil. And it also stimulated the increase of metabolic quotient, which indicated that the high application of myclobutanil increased the environmental stress on soil microbial community and decreased microbes’ carbon utilization efficiency at the same time. T1 and T3 caused different degrees of short-term inhibition of soil microbial basal respiration, soil microbial biomass C, the populations of total fungi and bacteria, but the effects were somewhat inconsistent and erratic. The effects of different concentrations of myclobutanil on Henan Fluvo-aquic soil microbes eliminated basically within a month. In Shanxi cinnamon soil, all the three different concentrations of myclobutanil had little effect on soil microbial basal respiration, biomass C, the populations of total fungi and bacteria and the metabolic quotient, which means myclobutanil didn’t pose environmental stress on Shanxi cinnamon soil. Myclobutanil was low toxicity to the two kinds of soil microbes within 10 times the recommended dose according to Test guidelines on environmental saf ety assessment f or chemical pesticides.3. The results of soil nitrogen transformations showed that different concentrations of myclobutanil had no effect on soil microbial N immobilization(soil microbial biomass N) in Fluvo-aquic soil, but all the three concentrations reduced the gene abundance of N2-fixing bacteria, ammonia-oxidizing bacteria and ammonia-oxidizing archaea. And myclobutanil only had short-term inhibition on soil NH+4-N and NO-3-N. The inhibition effects of myclobutanil on the nitrogen transformations in Henan Fluvo-aquic soil were eliminated within a month. In Shanxi cinnamon soil, high concentrations of myclobutanil(4 mg kg-1) decreased the soil microbial N immobilization in short-term and had no inhibition on nitrogen-fixing bacteria group. However, the populations of ammonia-oxidizing microorganisms was stimulated slightly under the middle and high concentrations of myclobutanil. It had no inhibition on soil NH+4-N but slightly stimulated the increase of NO-3-N. According to Test guidelines on environmental safety assessment for chemical pesticides, myclobutanil had no long-time inhibition effect on two kinds of soil nitrogen transformations within 10 times the field recommended dose, and it had few influence on soil nitrogen transformations.