Soil microbial communities in diverse agroecosystems exposed to glyphosate

In spite of glyphosates wide use in agriculture, questions remain about effects of the herbicide on soil microbial communities. Conflicting scientific literature reports divergent results; from no observable effect of glyphosate to the enrichment of common agricultural pathogens such as Fusarium. We conducted a comprehensive field-based study to compare treatments that did and did not receive foliar application of glyphosate spray. The study included two field sites, Maryland and Mississippi; two crops, soybean and corn; four site years, 2013 and 2014; and a variety of organic and conventional farming systems. Using amplicon sequencing, the prokaryotic (16S rRNA) and fungal (ITS) communities were described along with chemical and physical properties of the soil. Sections of corn and soy roots were plated to screen for the presence of plant pathogens. Geography, farming system, and seasonal progression were significant factors determining composition of fungal and bacterial communities. Plots treated with or without glyphosate did not differ in overall microbial community composition after controlling for these factors. No differential effect of glyphosate treatment was found in the relative abundance of organisms such as Fusarium spp. or putative growth-promoting bacteria Pseudomonas spp.