Glyphosate effects on soil rhizosphere-associated bacterial communities

Abstract

Glyphosate is one of the most widely used herbicides in agriculture with predictions that 1.35 million metric tons will be used annually by 2017. With the advent of glyphosate tolerant (GT) cropping more than 10 years ago, there is now concern for non-target effects on soil microbial communities that has potential to negatively affect soil functions, plant health, and crop productivity. Although extensive research has been done on short-term response to glyphosate, relatively little information is available on long-term effects. Therefore, the overall objective was to investigate shifts in the rhizosphere bacterial community following long-term glyphosate application on GT corn and soybean in the greenhouse. In this study, rhizosphere soil was sampled from rhizoboxes following 4 growth periods, and bacterial community composition was compared between glyphosate treated and untreated rhizospheres using next-generation barcoded sequencing. In the presence or absence of glyphosate, corn and soybean rhizospheres were dominated by members of the phyla Proteobacteria, Acidobacteria, and Actinobacteria. Proteobacteria (particularly gammaproteobacteria) increased in relative abundance for both crops following glyphosate exposure, and the relative abundance of Acidobacteria decreased in response to glyphosate exposure. Given that some members of the Acidobacteria are involved in biogeochemical processes, a decrease in their abundance could lead to significant changes in nutrient status of the rhizosphere. Our results also highlight the need for applying culture-independent approaches in studying the effects of pesticides on the soil and rhizosphere microbial community.

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

“…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). It was found that six different genera of cyanobacteria responded differently to glyphosate concentrations (from 0.03 to 10 mM) and the growth response ranged from no change to lethal effects (Forlani et al, 2008).…”

Re-registration Challenges of Glyphosate in the European Union

“…A recent study provides a Europe-wide assessment of the dispersal of glyphosate and AMPA in EU agricultural topsoils, being present in 45% of the topsoils collected, originating from 11 countries and six crop systems, with a maximum concentration of 2 mg/kg, as well as their potential spreading by wind and water erosion , further affected by small-scale sediment transport in water erosion (Bento et al, 2018), persisting under low bacterial activity in limited aerobic conditions or non-neutral pH (la Cecilia and Maggi, 2018), and adversely affecting soil microbial and nematodal diversity (Dennis et al, 2018). From the soil glyphosate can be translocated by plant roots; and it can affect non-target plants near agricultural ditches (Saunders and Pezeshki, 2015), and affect soil rhizosphere-associated bacterial communities (Newman et al, 2016) and soil Pseudomonas species (Aristilde et al, 2017). Toxicity of Roundup R to the soil filamentous fungus Aspergillus nidulans was reported with a median lethal dose (LD 50 ) corresponding to glyphosate concentrations of 90-112 mg/l, ∼100-fold below agricultural application levels (Nicolas et al, 2016).…”

Impact of Pesticides on Soil Microbial Diversity and Enzymes: A Review

“…They have reported increasing microbial population with the increase in insecticides namely endosulfan and profenofos of bacteria, fungi and actinomycetes up to recommended doses. Newman et al, 2016 have also reported increase in abundance of Proteobacteria but decrease in relative abundance of acidobacteria in corn rhizosphere samples.…”