Repeated glyphosate exposure induces shifts in nitrifying communities and metabolism of phenylpropanoids

ALLEGRINI, MARCO; GOMEZ, ELENA V; ZABALOY, MARÍA CELINA

SOIL BIOLOGY AND BIOCHEMISTRY

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2017 vol. 105 p. 206 - 2015

0038-0717

Glyphosate is the most used herbicide worldwide. Repeated applications are very common in the fielddue to increasing incidence of glyphosate resistant (GR) weeds. Although several studies have consideredthe effects of single applications, the information related with the impact of repeated applications on soilmicrobial communities is comparatively less.We designed a laboratory experiment at microcosm level toassess the impact of up to three applications of glyphosate on microbial communities of soils with (H)and without history (NH) of exposure to the herbicide. The overall bacterial community and a specificgroup, the ammonia-oxidizing bacteria (AOB), were considered. Control microcosms (no glyphosate) andthose with one, two or three applications of the active ingredient (AI, N-(phosphonomethyl)glycinepotassium salt) or a commercial formulation (CF, Roundup Full II) were sampled after the final application.A higher respiratory quotient (RQ) was detected with p-coumaric acid as C source for microcosmswith three applications (AI or CF) relative to the control. Estimations of abundance of amoA gene (AOB)and 16S rRNA gene (Eubacteria) using Quantitative Real Time PCR (qPCR) indicated no effects of threeapplications (AI or CF). However, significant differences were detected for the CF when the abundance ofAOB was related to Eubacteria. Additionally, a shift in the structure of AOB was detected after threeapplications of either the AI or the CF. Together these results reflect an impact of repeated exposure toglyphosate on bacterial groups involved in key processes for C and N cycling in soil.