Investigating the context dependence of ectomycorrhizal fungal species interactions: Competition or facilitation?

Background/Question/Methods

The outcomes of interactions among ectomycorrhizal fungi (EMF) are often affected by the environmental context in which they occur. Part of the reason for these environmental context-dependent results is that the trading dynamics between EMF and their hosts vary across different environments, which can lead to the promotion of some EMF species over others. To examine how light availability affected the interactions between EMF species as well as the performance of the host, we grew Pseudotsuga menziesii seedlings inoculated with the spores of two EMF species, Rhizopogon vinicolor and Truncocolumella citrina, individually as well as together at two light levels.

Results/Conclusions

We observed an increase in R. vinicolor abundance from single to two-species treatments.  This result was light-level independent, suggesting facilitation may be an important component of the early colonization dynamics in this system. Interestingly, there was no observed correlation between T. citrina abundance and R. vinicolor abundance, indicating that this putatively facilitative interaction was not driven by existing colonization of one of the species.  These results should be interpreted cautiously because colonization by R. vinicolor and T. citrina was at an early stage. A second harvest will occur in July and the results of both harvests will be represented at the ESA meeting.  If facilitation is still present in the second harvest, this study would indicate an exciting new direction for research on EMF interactions.