Microbial community composition and enzyme activities in a sandy loam soil after fumigation with methyl bromide or alternative biocides

A sandy loam soil was fumigated in microcosms for 24 It with methyl bromide and chloropicrin (MeBr + CP), propargyl bromide (PrBr), combinations of 1,3-dichloropropene and CP (InLine), iodomethane and CP (Midas), an emulsifiable concentrate of CP (CP-EC), or methyl isothiocyanate (MITC). The effects of these pesticides on fatty acid methyl ester (FAME) profiles and selected enzymatic activities were evaluated in fumigated soils and a nonfumigated control at 1, 3, 7, 14, 21, 28, and 90 days post-fumigation. Bacterial (a15:0, i15:0, i16:0, cy17:0, a17:0 and i17:0) and fungal (18:2 omega 6, 18:3 omega 6, 18:1 omega 9) FAMEs were initially (I day post-fumigation) 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 14-28 days post-fumigation, FAME profiles were changed in all fumigated soils relative to the control, with the exception of soils treated with MITC. At 90 days post-fumigation, FAME profiles suggested that actinomycetes (10 Me 16:0, 10 Me 17:0, 10 Me 18:0) and Gram-positive bacteria may recover preferentially after fumigation with most of the pesticides studied. Among the fumigants tested, InLine, Midas, and CP-EC had a higher potential to alter the microbial community structure in the longer term than MeBr + CP, PrBr and MITC, with MITC having the least effect. Soil enzyme activities in fumigated microcosms were significantly (P <= 0.037) different from the nonfurnigated soil, with the exception of beta-glucosidase in soils treated with PrBr and MITC, and dehydrogenase in MeBr+CP-fumigated soils. Over the 90-day study, soil fumigation (average of all fumigants and sampling dates) reduced the activities of arylsulfatase (62%), dehydrogenase (35%), acid phosphatase (22%), and beta-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. This study also indicates that soil fumigation with MeBr + CP alternative biocides has the potential to alter microbial communities and important key reactions involved in nutrient transformation. (c) 2006 Elsevier Ltd. All rights reserved.