Establishment Of Residue Detection Method Of Clomazone And Its Effect On Soil Microbial Community

Clomazone is mainly used in soybean fields to control the broadleaf weeds and the grass family weeds by its wide range,high activity and high selectivity.However,clomazone has a long half-life in soil and it may pose a potential threat to the security of soil microbial community structure and functions.In the present study,3-month-long incubation experiment of the greenhouse was carried out by using the silty-loam agricultural soil of Langfang.Soil was sampled after 7,15,30,60,90 days of incubation and we used next-generation sequencing combined with the real-time quantitative PCR to study the effects of three different concentrations of clomazone?1200 ga.i./hm²,T1;12000 ga.i./hm²,T10;120000 ga.i./hm²,T100?on the soil microbial community gene abundance,community structure,predominant groups,functional groups involved in nitrogen cycling.The results are as follows:In the work,the determination of clomazone residues in soil was conducted by the combined use of modified quick,easy,cheap,effective,rugged,and safe?QuChERS?preparetion procedure and ultra-performance chromatography?UPLC?.The method showed excellent lineary?r=0.9997?in therange of 0.5-100 mg/L.The mean recoveries from soil matrice spiked at 1 mg/kg?10 mg/kg?50mg/kg and 100 mg/kg were ranged from 85.1%to 106.5%with the intra-day relative standard deviations?RSDs?in the range of 0.92-7.97%.The degradation dynamics of different concentrations of clomazone in soil were all meet the the first-order kinetic equation.The half-lives of the different concentrations varied from 69.3 to 115.5 days in Langfang silty-loam.There was a tendency to promote bacterial gene abundance in three concentrations,and the bacterial gene abundance of T10 was the highest on the 15th day of incubation.The diversity index study found that clomazone inhibited the Shannon index of bacteria,and the inhibition was not eliminated in 90 days under the treatment of T100.The ACE and Chao1 indexes of the bacteria were significantly promoted at the 30th day of culture,and the rest time was not changed significantly.The results of PCoA showed that the bacterial community structure changed significantly under the treatment of T1,T10 and T100,and began to recover at 90 days.The effect of three concentrations of clomazone on the gene abundance of fungi was as follows:there was no obvious regularity in T1 treatment,and T10 treatment had the trend to promote the gene abundance of fungi at 30 days and 60 days of incubation.T100 treatment inhibited the fungal gene abundance significantly,and was significantly inhibited at 15 days of incubation.The diversity index study found that the three concentrations inhibited the Shannon index of fungi,which was significantly inhibited within 15 days.The treatments of T10 and T100 promoted the growth of fungal Simpson index,and the Simpson index of fungi was significantly promoted within 15 days in T10 treatment,the fungal Simpson index of T100 treatment was significantly promoted within 60days of incubation.The fungal ACE indexes of T10 and T100 were significantly inhibited at 7 days of incubation,and no significant changes were found in other time.The Chao1 indexes of fungi in T10and T100 were significantly inhibited.The results of PCoA showed that the bacterial community structure changed significantly under the treatment of T1,T10 and T100 and and began to recover at90 days.The results of nitrogen transformation showed that different concentrations of clomazone slightly inhibited the concentration of ammonium nitrogen,and significantly stimulated the concentration of nitrate nitrogen.The effects of three concentrations on the gene abundance of functional groups involved in nitrogen cycling were as follows:three concentrations of clomazone significantly promoted the abundance of ammonia-oxidizing bacteria during the whole culture period,the gene abundance of ammonia-oxidizing archaea and nitrogen-fixing bacteria all have the promotion trend.T10 significantly increased the gene abundance of ammonia-oxidizing archaea within 90 days,and T1 and T100 had no effect on the gene abundance of ammonia-oxidizing archaea within 30 days,the stimulation was produced at 60 days.These results indicated that clomazone may have enhanced the nitrification process by increasing the abundance of AOB and AOA,which may make NO₃^--N vulnerable to leaching and/or denitrification in the ecosystem.