The Degradation of Glyphosate and Its Effect on the Microbial Community of Agro-Sod–Podzolic Soil under Short-Term Model Experiment Conditions

Abstract

Under laboratory conditions, the decomposition of glyphosate with the formation of aminomethylphosphonic acid (AMPA) and its effect on the total abundance of bacteria and fungi as well as the number of copies of genes encoding the enzymes C–P lyase of α-proteobacteria (phnJ), acid and alkaline phosphatase (phoC and phoD) and Fe protein of nitrogenase (nifH) in agro-sod-podzolic soil (Epialbic Retisol) were determined. It was shown that when applying glyphosate in recommended doses (5–10 mg/kg), only 5–7% of the introduced herbicide were detected after 14 days, but when the dose was increased to 100 mg/kg, this value increased up to 23%. Decreasing the rate of the herbicide degradation was observed only during the first week of incubation and was accompanied by a decrease in the number of copies of the phoC, phoD, and nifH genes and an increase in the abundance of fungi. The obtained results indicate that glyphosate was mainly degraded by means of C–P bond breaking and the formation of phosphates, and also suggest possible inhibition of the nitrogen fixation process. It is shown that at an application dose of glyphosate of 100 mg/kg may lead to the accumulation of AMPA, the first metabolite of the herbicide degradation pathway, formed after the C–N bond break. Bioassay using wheat showed that when applying glyphosate at a dose of 100 mg/kg, an inhibition of plant development was observed: the length of the roots and the biomass of the shoots reduced by 60 and 20% compared to the control, respectively. Based on the data obtained, it was proposed to use the reduction in the content of copies of the phoC gene and the increase in the number of copies of ITS rRNA as indicators of the predominant decomposition of glyphosate through the sarcosine pathway. The decrease in the number of copies of ITS rRNA gene by 40% or more can be used as an indicator of the possibility of AMPA accumulation during glyphosate degradation.