Effects of the glyphosate-resistance gene and of herbicides applied to the soybean crop on soil microbial biomass and enzymes

Abstract

Glyphosate, a broad-spectrum herbicide used for the non-selective control of weeds, inhibits 5enolpyruvylshikimate-3-phosphate synthase, a key enzyme in the synthesis of aromatic amino acids in the shikimic acid pathway in plants, fungi and bacteria, thus impairing the synthesis of proteins required for various life processes. Soybean genetically engineered to be glyphosate resistant (GR or Roundup Ready, RR) represents the most cultivated transgenic crop globally, including Brazil. There are concerns about the effects of RR transgenic soybean and of glyphosate on soil microbial communities and their functioning. Our study was designed to detect changes in soil microbial biomass-carbon (MB-C) and-nitrogen (MB-N) and in enzyme activities [beta-glucosidase (GLU) and acid phosphatase (PHO)] in a large set of field trials performed at six sites in Brazil for two cropping seasons. We evaluated the effects of the RR transgene, glyphosate and weed management (RR soybean + glyphosate vs. conventional soybean + conventional herbicides), with three pairs of nearly isogenic soybean cultivars evaluated per site. Soils were sampled from the 0-10 cm layer, between cropped lines, during the cropping seasons 2004/2005 and 2005/2006, at the R2 stage of soybean growth. Univariate and contrast analyses were performed in addition to multivariate analyses including all four microbial variables, and denominated as soil microbial variables (SMV). In general, microbial parameters and SMV were not affected by the transgene, type of herbicide or weed management. Differences were, rather, related to site, cropping season and cultivar.

Response of soil phosphatases to glyphosate and its formulations - Roundup (laboratory conditions)

“…These results are in agreement with our previous studies (Płatkowski and Telesiński 2015a,b). The effect of glyphosate on soil enzymes involved in phosphorus metabolism gave conflicting results: inhibition (Sannino and Gianfreda 2001, Floch et al 2011, Yu et al 2011 and stimulation (Nakatani et al 2014, Cherni et al 2015. Tejada (2009) reported that the effect of glyphosate on phosphatases is higher in sandy soil than in clay soil.…”

Effect of different glyphosate salts on phosphodiesterase and phosphotriesterase activities in soil with reference to ecological importance of soil pollution. A laboratory experiment

“…3, 4). The effect of glyphosate on soil microorganisms depend on the dosage, soil texture and organic matter content [Giesy et al 2000, Nakatani et al 2014. The results obtained by Tejada [2009] showed that glyphosate effect on phosphatases is higher in light soil than in clay soil.…”

Comparison of glyphosate and Roundup preparations influence on inorganic pyrophosphatase activity and available phosphorus content in sandy loam

“…NPT.2016.1.13 7 (Płatkowski i Telesiński 2015a, 2015b. Wykonane dotychczas badania wskazują zarówno na brak zmian aktywności fosfataz glebowych pod wpływem glifosatu (Cherni i in., 2015;Nakatani i in., 2014), jak i na ich stymulację (Floch i in., 2011;Ying i in., 2011) czy inhibicję (Sannino i Gianfreda, 2001). Zmiany aktywności enzymów biorą-cych udział w przemianach związków fosforu w glebie są spowodowane obecnością w cząsteczce glifosatu grupy fosfonowej (Haney i in., 2000).…”