Soils harbor enormous biodiversity and understanding the causes of soil diversity and the impacts for ecosystem functioning is one of the major challenges in ecology. One of the best studied groups of soil organisms are the arbuscular mycorrhizal fungi (AMF), which are important plant symbionts. AMF play important roles in virtually all terrestrial ecosystems. The effects of the composition of AMF on plant competiveness, community composition and diversity are relatively well studied. Here, we focus on the reversed question: How does the surrounding vegetation influence the diversity and composition of the AMF community in individual plants?

We determined the composition of the AMF community in individual Tansy ragwort plants (Senecio jacobaea) growing in an experimental old-field site in sown and unsown plant communities. The plant communities were sown ten years earlier and were not weeded since, but developed into distinctly different communities. Within each of five replicate plant communities from both sowing treatments we randomly selected two individual ragwort plants and determined the AMF community composition in each plant using a molecular fingerprinting method, terminal restriction fragment length polymorphism (T-RFLP), combined with cloning and sequencing to identify the different AMF.

Results/Conclusions

A large number of TRF-peaks were found in individual ragwort plants and there were large differences between individual plants, but the composition of the AMF communities did not differ significantly between ragwort plants from sown or unsown plant communities. Unsown plant communities were much more spatially heterogeneous than sown ones. Remarkably, the AMF community composition of the two individual ragwort plants growing within the same plot was also four times less similar in unsown plant communities. In a greenhouse experiment, the AMF composition in individual ragwort plants growing in soil collected from the field, differed distinctly from the AMF community in plants directly growing in the field, and no difference in AMF community heterogeneity between sown and unsown plant communities was found anymore.

Our study clearly shows that there is a direct link between heterogeneity of the plant community and the heterogeneity of the soil community associated to individuals growing within the plant community in the field. Ragwort is native in the Netherlands, but considered a problematic and invasive species in America. We will discuss how neighboring plants, via their impact on soil organisms that interact with ragwort can influence the long-term dynamics of this noxious species.