13C assimilation as well as functional gene abundance and expression elucidate the biodegradation of glyphosate in a field experiment. (1st August 2022)

• Record Type: Journal Article
• Authors: Wirsching, Johannes; Wimmer, Benedikt; Ditterich, Franziska; Schlögl, Johanna; Martin-Laurent, Fabrice; Huhn, Carolin; Haderlein, Stefan; Kandeler, Ellen; Poll, Christian
• Is Part Of: Environmental pollution. Volume 306(2022)
• Publication Date: 2022-08-01
• Subjects: Glyphosate transfer -- Preferential flow pathways -- Structured soil -- Simulated heavy rainfall event -- Glyphosate biodegradation; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2022.119382
• Languages: English
• ISSNs: 0269-7491

Abstract

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% 13 C3, 15 N-labeled GLP one day before the simulated rainfall event. Microbial degradation of translocated GLP over a 21-day period was assessed by quantifying 13 C 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 10 5 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 13 C-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 13 C-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. Graphical abstract: Image 1 Highlights: Biodegradation of glyphosate via the AMPA pathway is prevalent in the bulk soil. Glyphosate degradation via the sarcosine pathway is enhanced in shrinkage cracks. Fungi appear to initiate glyphosate degradation. Gram positive bacteria are the major glyphosate degraders.