Effects of glyphosate on soil microbial communities and its mineralization in a Mississippi soil

Abstract

Transgenic glyphosate-resistant (GR) soybean [Glycine max (L.) Merr.] has enabled highly effective and economical weed control. The concomitant increased application of glyphosate could lead to shifts in the soil microbial community. The objective of these experiments was to evaluate the effects of glyphosate on soil microbial community structure, function and activity. Field assessments on soil microbial communities were conducted on a silt loam soil near Stoneville, MS, USA. Surface soil was collected at time of planting, before initial glyphosate application and 14 days after two post-emergence glyphosate applications. Microbial community fatty acid methyl esters (FAMEs) were analyzed from these soil samples and soybean rhizospheres. Principal component analysis of the total FAME profile revealed no differentiation between field treatments, although the relative abundance of several individual fatty acids differed significantly. There was no significant herbicide effect in bulk soil or rhizosphere soils. Collectively, these findings indicate that glyphosate caused no meaningful whole microbial community shifts in this time period, even when applied at greater than label rates. Laboratory experiments, including up to threefold label rates of glyphosate, resulted in up to a 19% reduction in soil hydrolytic activity and small, brief (<7 days) changes in the soil microbial community. After incubation for 42 days, 32-37% of the applied glyphosate was mineralized when applied at threefold field rates, with about 9% forming bound residues. These results indicate that glyphosate has only small and transient effects on the soil microbial community, even when applied at greater than field rates.

Glyphosate-Induced Specific and Widespread Perturbations in the Metabolome of Soil Pseudomonas Species

“…By contrast, the P. putida species were more sensitive to the glyphosate-containing growth media whereby, compared to growth in the absence of glyphosate, the strain S12 experienced up to 100% growth inhibition but the strain KT2440 only exhibited up to about 23% growth inhibition (Figure 2). There have been conflicting results on the adverse effects of glyphosate exposure on soil microbial community structure (Weaver et al, 2007;Johal and Huber, 2009;Kremer and Means, 2009;Mijangos et al, 2009;Barriuso et al, 2011;Duke et al, 2012). Our results here support the proposal that species-dependent sensitivities to glyphosate led to the observed change in microbial community structure in soils amended with glyphosate (Ratcliff et al, 2006;Newman et al, 2016).…”

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“…The reason for this observation was borne of the fact that the degradation of glyphosate was more rapid in the wet season than in the dry season which conforms to the finding of Smith and Aubin (1993) that the relative dryness of the soil in dry seasons may result to slow dissipation of glyphosate herbicide. Weaver et al (2007), reported that glyphosate herbicide dissipates rapidly when applied to moist soil than dry soil.…”

Herbicides in the Soil Environment: Linkage between Bioavailability and Microbial Ecology

“…No major changes in community structure, assessed by CLPP and PLFA, occurred with application of field rate concentrations of glyphosate in soils from two pine plantations in California (Ratcliff et al, 2006). Both higher abundance of PLFA biomarkers of gram-negative bacteria (Weaver et al, 2007;Lancaster et al, 2009) and fungal to bacterial biomass ratios ) have been reported in glyphosate-treated soils. In a recent study, Zabaloy et al (2009) reported minor effects of glyphosate on sole C sources utilization with BDOBS.…”

“…Unintended consequences of herbicide applications may be the reduction of sensitive populations and/or stimulation of a certain microbial group with or without detriment to co-existing microbial populations that may compete for available resources. Several investigations that used culture-independent methods reported only slight, short-lived effects of field levels of glyphosate (Weaver et al, 2007;Accinelli et al, 2007) and 2,4-D (Chinalia & Killham, 2006;Macur et al, 2007;Vieublé-Gonod et al, 2006) on microbial communities. No major changes in community structure, assessed by CLPP and PLFA, occurred with application of field rate concentrations of glyphosate in soils from two pine plantations in California (Ratcliff et al, 2006).…”