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Title:   Author  item
                                            KLOSE, SUSANNE - UNIV CA, DAVISitem
                                            Acosta-Martinez, Veronicaitem
                                            AJWA, HUSSEIN - UNIV CA, DAVIS
  Submitted to: Soil Biology and Biochemistry
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 9/28/2005
                                    Publication  Date: 11/8/2005
                                    Citation: Klose, S., Acosta Martinez, V., Ajwa, H. 2005. Microbial community composition and enzyme activities in a sandy loam soil after fumigation with methyl bromide and alternative biocides. Soil Biology and Biochemistry. 37(12):2171-2182.Interpretive Summary: Fumigation of soils with methyl bromide is a common practice to control nematodes, soil microbial pathogens, and weeds, but little is known about the effects of fumigant biocides on the soil microbial community and enzyme processes.  The manufacture and importation of methyl bromide will be completely phase out in 2005. Thus, our study investigated the impacts of the most promising biocides in replacing the standard MeBr + CP application on soil microbial functional and structural diversity at 1, 3, 7, 14, 21, 28, and 90 days past fumigation under laboratory conditions. A sandy loam soil was fumigated for 24 hours with the following 6 fumigants: (1) methyl bromide and chloropicrin (MeBr + CP), (2) propargyl bromide (PrBr), (3) a combination of 1, 3-dichloropropene and CP (InLine), (4) iodomethane (Midas), (5) an emulsifiable concentrate of CP (CP-EC), or (6) methyl isothiocyanate (MITC).  One day past fumigation the bacterial and fungal populations (indicated by fatty acids analyses) were reduced by fumigation with CP-EC, InLine, and Midas whereas the microbial communities of soils fumigated with MeBr + CP, MITC, and PrBr were similar to the control soil.  Fourteen and twenty eight days past fumigation, the microbial community was changed in all fumigated soils relative to the control, with exception of soils treated with MITC.  At ninety days past fumigation, actinomycetes and gram-positive bacteria recovered after fumigation with most of the pesticides studied.  This study showed that InLine, Midas and CP-EC have a higher potential to alter microbial community structure in the longer term than MeBr + CP, PrBr and MITC.  Over the 90-day study, soil fumigation reduced the activities of arylsulfatase (62%) and dehydrogenase (35%) more than acid phosphatase (22%) and '-glucosidase (6%) activities.  These findings suggested that S mineralization in soils and the total oxidative potential of microorganisms were more affected by fumigation than P and C mineralization.  Our results suggest that soil fumigation with MeBr + CP alternative biocides have the potential to alter microbial communities and important key reactions involved in nutrient transformation.
                                Technical Abstract: Fumigation of soils is a common agricultural, silvicultural, and horticultural practice to control nematodes, soil-borne pathogens and weeds, but little is known about the effects of fumigant biocides on the soil microbial community structure and enzymatic processes.  A sandy loam soil was fumigated in microcosms for 24 hours with methyl bromide and chloropicrin (MeBr + CP), propargyl bromide (PrBr), a combination of 1,3-dichloropropene and CP (InLine), iodomethane (Midas), an emulsifiable concentrate of CP (CP-EC), or methyl isothiocyanate (MITC). The effects of these pesticides on FAME profiles and the activities of '-glucosidase, acid phosphatase, arylsulfatase and dehydrogenase were evaluated in fumigated soils and a nonfumigated control at 1, 3, 7, 14, 21, 28, and 90 days past fumigation.  Bacterial (a15:0, i15:0, i16:0, cy17:0, a17:0 and i17:0) and fungal (18:2'6, 18:3'6, 18:1'9) FAMEs were initially (1 day past fumigation, 1 DPF) reduced by fumigation with CP-EC, InLine, and Midas. Microbial communities of soils fumigated with MeBr + CP, MITC, and PrBr resembled those of the control soil. At 14 to 28 DPF, FAME profiles were changed in all fumigated soils relative to the control, with exception of soils treated with MITC. Among the alternative fumigants studied, MITC had the least effect on the microbial community structure. At 90 DPF, FAME profiles suggested that actinomycetes (10Me 16:0, 10Me 17:0, 10Me 18:0) and gram-positive bacteria may recover preferentially after fumigation with most of the pesticides studied. Lack of recovery in FAME profiles in soils fumigated with InLine, Midas and CP-EC suggested that these fumigants have a higher potential to alter microbial community structure in the longer term than MeBr + CP, PrBr and MITC. The activities of acid phosphatase, arylsulfatase, '-glucosidase and dehydrogenase were significantly (P<0.001) affected by fumigation, sampling time (DPF), and the interactions between these two factors. Soil enzyme activities in microcosms fumigated with MeBr + CP and the five tested alternative biocides were significantly (P' 0.037) different from the nonfumigated soil, with exception of '-glucosidase in microcosms treated with PrBr and MITC, and dehydrogenase in MeBr + CP-fumigated soils. Over the 90-day study period, soil fumigation reduced the activities of arylsulfatase (62%), dehydrogenase (35%), acid phosphatase (22%), and '-glucosidase (6%), suggesting that S mineralization in soils and the total oxidative potential of microorganisms were more affected by fumigation than P and C mineralization. Results of this study suggest that soil fumigation with MeBr + CP alternative biocides has the potential to alter microbial communities and important key reactions involved in nutrient transformation.


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