Impact of field -grown genetically modified canola on the diversity of rhizosphere and root -interior microbial communities

Transgenic or genetically modified plants possess novel genes that impart beneficial characteristics such as herbicide resistance. Unfortunately there is a paucity of information on the interaction and impact of transgenic plants on the soil microbial community. A 3-year field study was conducted to assess the effects of herbicide-tolerant genetically modified canola on microbial communities. Four genetically modified and four non-genetically modified canola varieties were grown at six locations across Saskatchewan, Canada. The rhizosphere and root-interior microbial communities were characterized using community level physiological profiles (CLPP), fatty acid methyl ester analysis (FAME) and terminal amplified ribosomal DNA restriction analysis (T-ARDRA). The microbial communities associated with genetically modified canola varieties were significantly different than the microbial communities associated with conventional canola varieties. However, this effect was dependent on the transgene. In particular, the glyphosate-tolerant variety Quest supported a unique microbial community compared to the communities supported by the four conventional varieties and three glufosinate ammonium-tolerant varieties tested.;Analysis of rhizosphere microbial communities associated with canola throughout the field season demonstrated that these communities are subject to seasonal variation. Importantly, in April (after plants were harvested in the preceding September) no differences were observed between microbial communities from field plots that contained harvested transgenic canola stubble and field plots that contained no plants during the field season, demonstrating that the effect of transgenic plants on the microbial community was temporary.;The composition and functional diversity of microbial communities from fallow soil and rhizosphere and root-interior microbial communities associated with canola plants were significantly influenced by field site. Furthermore, field site interacted with plant variety in its influence on the microbial community. The effect of plant variety on the microbial community at one field site was sometimes entirely different in another field site. Therefore, generalizations about the effect of genetically modified plants on all soil microbial communities are not possible.;The interaction between microbial communities, transgenic plants and field site, along with the season variability in microbial communities documented in this study emphasizes the complexity and need for a multifaceted approach to study the risks of transgenic plants to the diversity of the microbial community.