Separating the effect of crop from herbicide on soil microbial communities in glyphosate-resistant corn

Glyphosate-resistant (GR) cropping systems change the soil environment by introducing novel compounds and glyphosate into the soil environment. Over one growing season, we examined the effect of both the transgenic corn and the use of glyphosate on two groups of rhizosphere microbes, denitrifying bacteria and fungi. Using quantitative PCR to measure microbe abundance, and terminal restriction fragment length polymorphism (T-RFLP) to measure community structure, we found neither crop type (transgenic or conventional) nor herbicide (glyphosate or conventional) affected rhizosphere denitrifying or fungal communities. Instead, our results showed that seasonality was a significant determinant of denitrifier and fungal abundance as well as their diversity in this study, suggesting in the short term, some microbial communities are robust to changes in their environment by GR crops.