title: Effects of repeated glyphosate applications on soil microbial community composition and the mineralization of glyphosate.
abstract: BACKGROUND
  Repeated applications may have a greater impact on the soil microbial community than a single application of glyphosate. Experiments were conducted to study the effect of one, two, three, four or five applications of glyphosate on soil microbial community composition and glyphosate mineralization and distribution of (14)C residues in soil.
  
  
  RESULTS
  Fatty acid methyl esters (FAMEs) common to gram-negative bacteria were present in higher concentrations following five applications relative to one, two, three or four applications both 7 and 14 days after application (DAA). Additionally, sequencing of 16S rRNA bacterial genes indicated that the abundance of the gram-negative Burkholderia spp. was increased following the application of glyphosate. The cumulative percentage (14)C mineralized 14 DAA was reduced when glyphosate was applied 4 or 5 times relative to the amount of (14)C mineralized following one, two or three applications. Incorporation of (14)C residues into soil microbial biomass was greater following five glyphosate applications than following the first application 3 and 7 DAA.
  
  
  CONCLUSIONS
  These studies suggest that the changes in the dissipation or distribution of glyphosate following repeated applications of glyphosate may be related to shifts in the soil microbial community composition.
authors.affiliation: Department of Soil and Crop Sciences, Texas A&M University System, College Station, TX, USA. sarah.lancaster@okstate.edu
authors.forename: Sarah H
authors.initials: SH
authors.lastname: Lancaster
authors.forename: Emily B
authors.initials: EB
authors.lastname: Hollister
authors.forename: Scott A
authors.initials: SA
authors.lastname: Senseman
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Gentry
mesh_terms: D018533:Biomass; D002250:Carbon Radioisotopes / Q000032:analysis; D004269:DNA, Bacterial / Q000032:analysis; D020459:Genes, rRNA; D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry; D006090:Gram-Negative Bacteria / Q000378:metabolism; D006540:Herbicides / Q000737:chemistry*; D012987:Soil / Q000032:analysis*; D012988:Soil Microbiology; D000097797:Glyphosate
chemical_list: D002250:Carbon Radioisotopes; D004269:DNA, Bacterial; D005998:Glycine; D006540:Herbicides; D012987:Soil; D000097797:Glyphosate