13C assimilation as well as functional gene abundance and expression elucidate the biodegradation of glyphosate in a field experiment

Johannes Wirsching; Benedikt Wimmer; Franziska Ditterich; Johanna Schlögl; Fabrice Martin-Laurent; Carolin Huhn; Stefan Haderlein; Ellen Kandeler; Christian Poll

doi:10.1016/j.envpol.2022.119382

¹³C assimilation as well as functional gene abundance and expression elucidate the biodegradation of glyphosate in a field experiment

Environ Pollut. 2022 Aug 1:306:119382. doi: 10.1016/j.envpol.2022.119382. Epub 2022 May 4.

Authors

Johannes Wirsching¹, Benedikt Wimmer², Franziska Ditterich³, Johanna Schlögl⁴, Fabrice Martin-Laurent⁵, Carolin Huhn², Stefan Haderlein⁴, Ellen Kandeler³, Christian Poll³

Affiliations

¹ Soil Biology Department, Institute of Soil Science and Land Evaluation, University of Hohenheim, Emil-Wolff-Str. 27, 70599, Stuttgart, Germany. Electronic address: johannes.wirsching@uni-hohenheim.de.
² Institute for Physical and Theoretical Chemistry, Eberhard Karls University, Tübingen, Germany.
³ Soil Biology Department, Institute of Soil Science and Land Evaluation, University of Hohenheim, Emil-Wolff-Str. 27, 70599, Stuttgart, Germany.
⁴ Center of Applied Geosciences, Environmental Mineralogy and Chemistry, Eberhard Karls University, Tübingen, Germany.
⁵ INRAE, Institut Agro Dijon, Université de Bourgogne, Université de Bourgogne Franche-Comté, Agroécologie, Dijon, France.

PMID: 35525509
DOI: 10.1016/j.envpol.2022.119382

Abstract

Glyphosate (N-phosphonomethylglycine; GLP) and its main metabolite AMPA (aminomethylphosphonic acid), are frequently detected in relatively high concentrations in European agricultural topsoils. Glyphosate has a high sorption affinity, yet it can be detected occasionally in groundwater. We hypothesized that shrinkage cracks occurring after dry periods could facilitate GLP transport to greater depths where subsoil conditions slow further microbial degradation. To test this hypothesis, we simulated a heavy rainfall event (HRE) on a clay-rich arable soil. We applied 2.1 kg ha^-1 of 100% ¹³C₃, ¹⁵N-labeled GLP one day before the simulated rainfall event. Microbial degradation of translocated GLP over a 21-day period was assessed by quantifying ¹³C incorporation into phospholipid fatty acids. Microbial degradation potential and activity were determined by quantifying the abundance and expression of functional genes involved in the two known degradation pathways of GLP; to AMPA (goxA) or sarcosine (sarc). We confirmed that goxA transcripts were elevated in the range of 4.23 x 10⁵ copy numbers g^-1 soil only one day after application. The increase in AMPA associated with a rise in goxA transcripts and goxA-harboring microorganisms indicated that the degradation pathway to AMPA dominated. Based on ¹³C-enrichment 3 h after the HRE, fungi appeared to initiate glyphosate degradation. At later time points, Gram⁺-bacteria proved to be the main degraders due to their higher ¹³C-incorporation. Once GLP reached the subsoil, degradation continued but more slowly. By comparing GLP distribution and its microbial degradation in macropores and in the bulk soil, we demonstrated different time- and depth-dependent GLP degradation dynamics in macropores. This indicates the need for field studies in which soil properties relevant to GLP degradation are related to limiting environmental conditions, providing a realistic assessment of GLP fate in soils.

Keywords: Glyphosate biodegradation; Glyphosate transfer; Preferential flow pathways; Simulated heavy rainfall event; Structured soil.

MeSH terms

Glycine / analogs & derivatives
Glyphosate
Herbicides* / analysis
Soil
Soil Pollutants* / analysis
alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid

Substances

Herbicides
Soil
Soil Pollutants
alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid
Glycine