Effects Of Fomesafen On The Soil Microbial Diversity

Fomesafen, as selective post-emergence herbicide, are used agriculturally for broad-leaved weedscontrol in soybean field in China. However, fomesafen degrades slowly in soils and has been linked tocrop damage. The long-term pesticide residues lead to decline of the quality of soil. The changes ofmicrobial diversity directly reflect the health of the soil ecosystem. In this work, I focus on cultureexperiments, field investigation of contaminated soil and using microbial indicators of system of soilhealth evaluation, and the project clarify the microbiology mechanism of long residual herbicidefomesafen on soil health from the intensity of soil respiration, soil microbes microbial biomass carbon,community structure and functional diversity. The results are as follows:1: An effective and rapid analytical method for the determination of fomesafen residues in soilwas developed by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS)using the modified quick, easy, cheap, effective, rugged, and safe （QuEChERS） extraction concept.The fomesafen was extracted from soil matrices with0.5%(V/V) formic acid aqueous solution andacetonitrile then cleaned by dispersive solid phase extraction (dSPE) with PSA. The determination ofthe fomesafen was achieved within a5minute run time by using an UPLC C18column connected to anelectrospray ionization source (ESI, negative ion mode). The method showed excellent linearity (r=0.9945). The mean recoveries from soil matrices ranged from91.5to100.3%, with intra-day relativestandard deviations (RSDr) in the range of5.9～11.7%. The proposed method is a useful tool in routinefomesafen residue monitoring in soil.2: Culture experiments was conducted to evaluate the impact of different concentrations offomesafen on [1-fold,10-fold, and100-fold of the recommended field rate (T1, T10, T100)] on soilmicrobial activity, the structure of the soil microbial community, and functional diversity of the soilmicrobial community using the soil microbial respiration, microbial biomass, phospholipid fatty acids(PLFAs), community level physiological profiles (CLPPs), and real-time PCR in two different soils.Soil sampling was performed after7,15,30,60, and90days of application to determine the fomesafenconcentration. Fomesafen degradation appeared to consist of a rapid initial phase and a slower or morestagnant second phase. Our results indicate that applying100times the recommended dose offomesafen (T100) adversely affects soil microbial activity and stresses soil microbial communities asreflected by the reduced respiratory quotient (qCO2, QR). The PLFA analysis showed that high levels offomesafen treatment (T100) decreased the total amount of PLFAs and both bacterial (bothGram-positive (GP) bacteria and Gram-negative (GN) bacteria) and fungal biomass but increased themicrobial stress level. However, the BIOLOG results are not consistent with our other results. Theaddition of fomesafen significantly increased the average well color development, substrate utilization,and the functional diversity index (Shannon, McIntosh and Simpson). Additionally, the abundance ofthe nifH (N2-fixing bacteria) gene was reduced in the presence of high concentrations of fomesafen (T100). Taken together, these results suggest that the addition of fomesafen can alter the microbialcommunity structure and functional diversity of the soil, and these parameters do not recover even aftera90-day incubation period.3: Fomesafen has been widely used for the soybean production of China, but less information isavailable on the possible risk of long-term application of fomesafen. Soil samples were collected fromthe plots having been received375g active component of fomesafen/ha per year for3,5and10yearsin a continuously cropped soybean field of Northeast China with their microbial biomass, the structureof the soil microbial community, and functional diversity of the soil microbial community analyzed byphospholipid fatty acids (PLFAs) and community level physiological profiles (CLPPs). The microbialbiomass and total PLFA were suppressed with the increasing year of fomesafen application. Analysis ofthe PLFA profiles revealed that Gram-negative (GN), the GN/GP ratio and as well as total fungi in soilwith3,5and10year history of fomesafen application were much higher than blank soil. However, thebacterial biomass, Gram-positive (GP) bacteria and bacteria/fungi (B/F) had a significant decrease in theplot having been received fomesafen for10years. A principal component analysis (PCA) of the PLFAsrevealed that fomesafen treatment significantly shifted the microbial community structure. However,regarding AWCD, Shannon, McIntosh and Simpson, no clear differences were observed betweenfomesafen treatments and controls.