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Applied and Environmental Microbiology, July 2001, p. 3245-3257, Vol. 67, No. 7
George E. Brown Jr. Salinity Laboratory, USDA
Agricultural Research Service, Riverside, California
92507,1 and Department of
Environmental Sciences, University of California, Riverside, California
925212
Received 20 December 2000/Accepted 10 April 2001
Agricultural soils are typically fumigated to provide effective
control of nematodes, soilborne pathogens, and weeds in preparation for
planting of high-value cash crops. The ability of soil microbial communities to recover after treatment with fumigants was examined using culture-dependent (Biolog) and culture-independent (phospholipid fatty acid [PLFA] analysis and denaturing gradient gel
electrophoresis [DGGE] of 16S ribosomal DNA [rDNA] fragments
amplified directly from soil DNA) approaches. Changes in soil
microbial community structure were examined in a microcosm experiment
following the application of methyl bromide (MeBr), methyl
isothiocyanate, 1,3-dichloropropene (1,3-D), and chloropicrin.
Variations among Biolog fingerprints showed that the effect of MeBr on
heterotrophic microbial activities was most severe in the first week
and that thereafter the effects of MeBr and the other fumigants were
expressed at much lower levels. The results of PLFA analysis
demonstrated a community shift in all treatments to a community
dominated by gram-positive bacterial biomass. Different 16S rDNA
profiles from fumigated soils were quantified by analyzing the DGGE
band patterns. The Shannon-Weaver index of diversity,
H, was calculated for each fumigated soil sample. High
diversity indices were maintained between the control soil and the
fumigant-treated soils, except for MeBr (H decreased from 1.14 to 0.13). After 12 weeks of incubation, H
increased to 0.73 in the MeBr-treated samples. Sequence analysis of
clones generated from unique bands showed the presence of taxonomically unique clones that had emerged from the MeBr-treated samples and were
dominated by clones closely related to Bacillus spp. and Heliothrix oregonensis. Variations in the data were much
higher in the Biolog assay than in the PLFA and DGGE assays, suggesting a high sensitivity of PLFA analysis and DGGE in monitoring the effects
of fumigants on soil community composition and structure. Our results
indicate that MeBr has the greatest impact on soil microbial
communities and that 1,3-D has the least impact.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.7.3245-3257.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Impact of Fumigants on Soil Microbial
Communities
*
Corresponding author. Mailing address: USDA-ARS-George
E. Brown Jr. Salinity Lab., 450 W. Big Springs Rd., Riverside, CA
92507. Phone: (909) 369-4828. Fax: (909) 342-4963. E-mail:
aibekwe{at}ussl.ars.usda.gov.
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