Arbuscular mycorrhizal fungi (AMF) colonize the roots of most plants, but little is known about how AMF affect soil carbon cycling.  Previous research has shown that the presence of AMF can accelerate decomposition of plant detritus, even though AMF themselves do not have saprotrophic capabilities.  We hypothesized that AMF alter the microbial communities involved in decomposing plant material.  To test this hypothesis, chopped Plantago lanceolata roots were placed in soil separated from live P. lanceolata roots inoculated with Glomus hoi in sterile sand terragreen.  The two chambers were separated by 20- or 0.45-micron mesh to either include or exclude AMF.  The soil containing the decomposing root debris was destructively sampled after 40 days when microscopic observations confirmed that AMF had fully colonized the decomposing root debris.  The archaeal and bacterial communities present in the root debris soil were analyzed using PhyloChip high-density microarrays.  Universal bacterial, archaeal, and group specific 16S markers were quantified by qPCR to determine if changes in community composition were accompanied by changes in 16S copy number.  
Results/Conclusions

Ordination (NMS) of the microarray intensity values showed that the communities cluster based on the presence or absence of AMF, and that the separation was statistically significant using MRPP.  Quantitative PCR detected no significant response in bacterial 16S copy number in the presence of AMF; archaeal 16S copy numbers were slightly but significantly higher in the presence of AMF.  Primers designed to target groups identified by PhyloChip validated the increase of OTU 7778, which is taxonomically most similar to the family Ralstoniaceae, but were not able to detect significant results for general Lactobacillales and Comamonadaceae groups.  These results indicate that the presence of AMF does cause small population changes in the complex soil microbial community that can be quantified by high-density microarray analysis of community 16S RNA.