Effects Of Trifluralin On The Soil Microbial And Nitrogen Cycling

Trifluralin,as the dinitroaniline-selective pre-emergence herbicide,is mainly used to control monocotyledon weeds and annual broadleaf weeds in soybean fields and cotton fields.Trifluralin degraded slowly in soil,and it may be harmful to soil microbial and soil N cycle.In this subject,we performed indoor culture experiments and greenhouse experiments,and combined qPCR and next-generation sequencing(NGS)to investigate the effects of trifluralin on soil microorganisms and N cycles in soil.Two typical soybean field soils in China have been collected to carry out the indoor experiment,silty loam from Langfang(LF-silty loam)and silty clay from Jiansanjiang(JSJ-silty clay).Four treatment doses were prepared:0 mg kg-1(active ingredients per soil dry weight;CK),0.84 mg kg-1(a.i./dw;T1),8.4 mg kg-1(a.i./dw;T10),84 mg kg-1(a.i./dw;T100),and we collected samples on days 7,15,30,60,and 90.Silty loam from Langfang has been used to carry out the greenhouse experiments,four treatment doses were prepared:0 mg kg-1(active ingredients per soil dry weight;CK),1260 g ha-1(active ingredients per soil dry weight;T1),12600 g ha-1(a.i./dw;T10),126000 g ha-1(a.i./dw;T100),and we collected samples on days 7,15,30,60,and 90.The following contents have been detected and analized to evaluate the effects of trifluralin on soil microbes and N cycle:the trifluralin residue in soils,the abundance of bacteria and fungi,bacterial and fungal community composition and community structure,soil NH4+-N and NO3--N and functional groups(N2-fixing bacteria,ammonia-oxidizing bacteria and archaea)involved in Nitrogen cycling.The main research contents are as follows:1.A simple and rapid method for the detection of trifluralin residue in soil was established.Trifluralin in soil was extracted by acetone and detected by gas chromatography-electron capture detector.The calibration curves indicate a TFL concentration range of 0.10-20 mg kg-1 in soil,with a correlation coefficient of>0.99.The fortification experiment at 0.08,0.8,8,and 80 mg kg-1 soil was carried out.The average TFL recovery was 89.15-101.21%,with relative standard deviations of 1.98-8.21%.These data suggest that this method can be used to detect the TFL residue and study its degradation in soil.2.In indoor culture experiments,trifluralin was degraded faster in JSJ-silty clay than in LF-silty loam,the half-lives were 46,44 and 44 days(T1,T10,T100)in JSJ-silty clay and 69,58 and 52 days(T1,T10,T100)in LF-silty loam.It was degraded rapidly in the first 30 days in two type soils,and then degraded slowly.Bacterial abundances increased 0.92-20.18 times in LF-silty loam,and 0.091-3.92 times in JSJ-silty clay.But the bacterial community compositions and bacterial community structures were obviously impacted.The fungal abundances were inhibited 12.23-56.93%in LF-silty loam,and 33.13-69.67%in JSJ-silty clay.But the fungal community compositions and bacterial community structures were obviously impacted.The content of NH4+-N in these two soils were impacted,and NO3--N content were obviously inhibited.The functional groups involved in N Cycling were also impacted.N2-fixing bacteria were initially increased(the first 15 days),then decreased(30 to 60 days),and then recovered(90 days),and it was positively correlated with NH4+-N content.Ammonia-oxidizing bacteria and archaea were inhibited by trifluralin in two type soils.Ammonia-oxidizing bacteria were inhibited 25.52-92.64%in LF-silty loam,and 30.15-83.36%in JSJ-silty clay.Ammonia-oxidizing archaea were inhibited 20.21-65.73%in LF-silty loam,and 17.10-85.21%in JSJ-silty clay.3.LF-silty loam was selected to carry out the greenhouse experiments.The half-lives were 15,23 and 21 days for the three dosages.The bacterial abundance in T1 treatments was not impacted,it was significantly increased after day 60 in T10,and it was increased 0.33-0.67 times after day 15 in T100.Compared with the CK,the abundance of fungi was inhibited 30.72-42.26%.The bacterial community structures were impacted at day 15 and 60,and the fungal community structures were impacted at day 7,15 and 30.The contents of NH4+-N and NO3--N were also not influenced.The abundance of N2-fixing bacteria was significantly increased by trifluralin at day 15 and day 90.The abundance of ammonia-oxidizing archaea was not impacted,but the abundance of ammonia-oxidizing archaea was inhibited.