Arbuscular mycorrhizal fungi (AMF) form spatially complex communities in terrestrial ecosystems with known consequences for plant community structure and soil processes. It has previously been demonstrated that AMF community subsets differentially associate with host plants in a given community, but factors driving these relationships remain unclear. Here we examine potential influences on AMF community assembly in plant roots. Our first experiment involved alteration of nutrients (N and P) to two plant species, Centaurea stoebe (spotted knapweed) and Fescue idahoensis (idaho fescue) growing in a high sand/low nutrient media. We hypothesized that with shifts in nutrient acquisition strategy plants will associate with, or differentially utilize, different subsets of the AMF community. Since spatial and temporal relationships between AMF and host plants can influence the time at which seedlings are exposed to different subsets of an AMF community, we also examined the influence of individual AMF species on subsequent AMF community assemblage in plant roots. This experiment involved initial inoculation of Leucanthemum vulgare (oxeye daisy) seedlings with one of each of four different AMF genera prior to exposing the plants to soil containing a natural, mixed AMF community. For both experiments root inhabiting AMF communities were examined using AMF-specific T-RFLP analyses.

Results/Conclusions

Results for our first experiment indicate significant changes in root inhabiting AMF communities associated with F. idahoensis with altered nutrient availability, but not for C. stoebe. At low nutrient concentrations, AMF communities associated with the two plant species were not significantly different. This result suggests that when nutrient availability is low the potential for AMF-facilitated interaction between the two plant species may be greatest.

Results for the second experiment indicate that all four AMF genera used as inoculants were not only maintained in the presence of whole soil inoculum but had spread throughout the root system of each plant. Results of this experiment indicate that the identity of AMF species to which L. vulgare seedlings are initially exposed strongly influenced AMF community composition of the plants as they mature.