| As a sort of wide-spectrum fungicides,application of fumigants to agricultural soils before planting of high-value cash crops has been widely accepted by agriculture-related practitioners for decades due to its high efficiency in controlling soilborne pathogens,nematodes,rodents and weeds,but recently concerns have been raised over its pollution to the environment and potential hazards to the human health that might in turn influence the whole balance of ecosystem. To assess the influence of fumigants on soil quality,studies were conducted concerning its impact on soil microbial community function and structure.The results were summarized as follows:1. Soils were sampled from experimental plots of Chinese Academy of Agricultural Sciences,Tongzhou District ,Beijing.Microbial functional diversity and functional resilience after chloropicrin application were estimated with BIOLOG Eco-microplates.The results showed that the richness,evenness and diversity of soil microorganisms ,to some extent,were affected after chloropicrin treatment.The fact that the McIntosh index after chloropicrin application decreased by 72.31%,95.73% and 97.33% respectively in contrast to control soils indicated that species evenness were influenced while the magnified effects were observed as concentration increased.The Simpson index decreased by 39.36%,45.93% and 21.96% respectively showed the reduction of biodiversity after chloropicrin application.Soil Shannon index increased by 6.66% after application with 80mg/kg chloropicrin in contrast to control soils while the index differed less significantly with controls after treatment with 800mg/kg chloropicrin,which demonstrated that microbial functional diversity recovered,biomass and richness of microorganisms rising as concentration increased.Sampling after 7 days showed that all three indics fluctuated as time passed.McIntosh index decreased slightly after treatment with 40mg/kg chloropicrin,but figures rised after treatment with 80mg/kg and 800mg/kg.Simpson diversity indices of soil treated with three concentration gradients dropped less significantly.Shannon richness indics decreased in all treatments.AWCD and diversity index,such as Shannon,McIntosh and Simpson indics can be used to indicate the functional resistance to stress of chloropicrin.The fact that McIntosh evenness index whose tendency is in agreement with AWCD during the application can indicate the microbiology change of polluted environment showed that the best results can be obtained by using AWCD and McIntosh.2. Soil microorganisms metabolized mainly using carbonhydrates and amino acids as basic carbon sources.An obvious inhibitory effect was observed in microbial utilization of carbon substrates after the first introduction of chloropicrin.As increasing of incubation time,the decreased inhibitory effect of chloropicrin to microbial utilization of carbon substrates was observed due to the gradual adaptation of soil microbial community to chloropicrin.Soil dominant species multiplied substantially while the utilization type of microorganisms to carbon substrates increasing gradually.As comsuption of endogenous carbon source in soil,microbial species dropped functionally that resulted in the decrease of diversity and utilization of carbon substrates existing in Biolog wells.80mg/kg and 800mg/kg chloropicrin exerted strongly influence on uitilization of amino acids,carboxylic acids and amides. microbial physiological metabolism activity and carbon-metabolic species varied significantly and unique microbial communities were shaped in respective four soil samples.3. The effects of the applications of chloropicrin and sulfuryl fluoride on the change of microbial community structure exposed to two fumigants was studied under microcosm conditions using phospholipid fatty acid analysis(PLFA).The results showed that in control soils PLFAs within carbon number from 13 to 20 were detected,including saturated fatty acids(16:0,18:0,20:0),branched chain fatty acids(i13:0,a14:0,i15:0,i16:0,a16:0,9Me18:0),cyclopropane fatty acid(cy18:0),monounsaturated fatty acids(16:1ω7c,18:1ω9c) and polyunsaturated fatty acids(18:2ω6,9,22:4,20:3).The results based on the mole percentage of gross fatty acids showed that saturated fatty acids within even carbon number,which were the most abundant fatty acids type in soils,accounted for 41.97%.The contents of monounsaturated fatty acids and branched chain fatty acids which accounted for 29.18% and 13.22% respectively were relatively small in amount.Of those,saturated fatty acids(16:0,18:0),monounsaturated fatty acids(18:1ω9c,16:1ω7c) and brached chain fatty acid(a14:0) were dominant fatty acids.Polyunsaturated fatty acids were less popular accounting for merely 9.76%;and cyclopropane fatty acid accounting for less than 5% was the lowest proportion of gross fatty acids.Analysing the specific fatty acids indicated that in our study areas of agroecosystem, fungus were in large proportion and the dominant species were aerobic bacteria at depths from 5 to 20cm in the subsurface soil.4. Influene of chloropicrin and sulfuryl fluoride on soil microbial community structure was different to the extent.The study found that in soils treated with fumigants the relative contents of the fatty acids a14:0,i15:0 and i16:0 generally referred to as the biomarkers of Gram-positive bacteria, 16:1ω7c referred to the biomarkers of Gram-negative bacteria and the biomarkers of fungi, 18:2ω6,9 had decreased,while the reduction of the ratio of i15:0/16:0 in soils treated with 544mg/kg sulfuryl fluoride and chloropicrin,by 73.4% and 59.8% respectively,had been observed as to assume that gaseous sulfuryl fluoride had stronger lethality to bacteria than liquid chloropicrin. Meanwhile, after application of sulfuryl fluoride and chloropicrin, 16:1ω7c(Gram-negative bacteria) had decreased by 79% and 84% respectively, a14:0,i15:0 and i16:0(Gram-positive bacteria) had decreased by 51.7% and 68.4% respectively.The results showed that under stress of fumigants the survival rate of Gram-positive bacteria was higher than Gram-negative bacteria.
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