title: Soil ecotoxicity assessment of glyphosate use under field conditions: microbial activity and community structure of Eubacteria and ammonia-oxidising bacteria.
abstract: BACKGROUND
  A plot-scale experiment was conducted to assess the impact of field application rates of glyphosate on soil microbial communities by taking measurements of microbial activity (in terms of substrate-induced respiration and enzyme activity) in parallel with culture-independent approaches to assessing both bacterial abundance and diversity. Two rates of glyphosate, alone or in a mixture with 2,4-dichlorophenoxyacetic acid, were applied directly onto the soil surface, simulating normal use in chemical fallow in no-till systems.
  
  
  RESULTS
  No consistent rate-dependent responses were observed in the microbial activity parameters investigated in the field plots that were exposed to glyphosate. Denaturant gradient gel electrophoresis (DGGE) of the overall bacterial community (Eubacteria) and ammonia-oxidising bacteria (AOB) revealed no effects of the high rate of glyphosate on the structure of the communities in comparison with the control. No treatment effects were observed on the abundance of Eubacteria shortly after treatment in 2010, while a small but significant difference between the high rate and the control was detected in the first sampling in 2011. The abundance of AOB was relatively low during the study, and treatment effects were undetectable.
  
  
  CONCLUSIONS
  The absence of negative effects on soil microbial communities in this study suggests that glyphosate use at recommended rates poses low risk to the microbiota.
authors.affiliation: Microbial Ecology Laboratory, Departamento de Agronomía (UNS), Centro de Recursos Naturales Renovables de la Zona Semiárida (CERZOS), Bahía Blanca, Argentina.
authors.forename: María C
authors.identifier: http://orcid.org/0000-0003-1155-292X
authors.initials: MC
authors.lastname: Zabaloy
authors.affiliation: Facultad de Ciencias Agrarias, Universidad Nacional de Rosario, 2125, Zavalla, Argentina.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Carné
authors.affiliation: Facultad de Ciencias Agrarias, Universidad Nacional de Rosario, 2125, Zavalla, Argentina.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Viassolo
authors.affiliation: Microbial Ecology Laboratory, Departamento de Agronomía (UNS), Centro de Recursos Naturales Renovables de la Zona Semiárida (CERZOS), Bahía Blanca, Argentina.
authors.forename: Marisa A
authors.initials: MA
authors.lastname: Gómez
authors.affiliation: Facultad de Ciencias Agrarias, Universidad Nacional de Rosario, 2125, Zavalla, Argentina.
authors.forename: Elena
authors.initials: E
authors.lastname: Gomez
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000633:toxicity; D000641:Ammonia / Q000378:metabolism*; D001419:Bacteria / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D004347:Drug Interactions; D005998:Glycine / Q000031:analogs & derivatives* / Q000633:toxicity; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000633:toxicity*; D000097797:Glyphosate
chemical_list: D015084:2,4-Dichlorophenoxyacetic Acid; D000641:Ammonia; D005998:Glycine; D010088:Oxidoreductases; D012989:Soil Pollutants; D000097797:Glyphosate
keywords: ammonia-oxidising bacteria; denaturant gradient gel electrophoresis; glyphosate; microbial activity; quantitative PCR; soil microbial community