Journal
APPLIED SOIL ECOLOGY
Volume 46, Issue 2, Pages 240-246Publisher
ELSEVIER
DOI: 10.1016/j.apsoil.2010.08.006
Keywords
2,4-Dichlorophenoxyacetic acid; Degrading bacteria; BD Oxygen Biosensor System; CLPP; PICT
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Funding
- USDA through a CREES NRI [2006-35107-17226]
- South National University (UNS, Argentina) [PGI24/A12]
- National Council of Scientific and Technological Research (CONICET, Argentina)
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The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) may influence soil microbial communities by altering the balance between resident populations. Our objective was to assess the effect of environmentally relevant levels (ERLs) of 2,4-D on microbial community function and on the population dynamics of 2,4-D degrading bacteria using a microcosm approach. The most probable number approach was used to enumerate 2,4-D-degrading soil bacteria. Carbon substrates utilization was tested with a microtiter-based oxygen sensor system to evaluate short-term functional shifts caused by herbicide treatment. Shifts in the community in response to potential toxicity of 2,4-D were assessed in the agricultural soil and a reference forest soil using the pollution-induced community-tolerance (PICT) approach. Results indicated that the agricultural soil had a stable 2,4-D degrading population able to use the herbicide as C and energy source, which increases immediately after an ERL dose of 2,4-D and remains high for about 1 month after exposure has ceased. An enhanced, dose-dependent response to 2,4-D as substrate was observed in the microtiter assay, while heterotrophic bacterial activity appeared mostly unchanged. The PICT assay showed higher tolerance to 2,4-D in the agricultural soil than in the unexposed forest soil. Our results suggest that agricultural use of 2,4-D at recommended level leads to selection for (1) a copiotrophic degrader population and (2) a persistently herbicide-tolerant, but functionally similar, microbial community. (C) 2010 Elsevier B.V. All rights reserved.
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