Despite the importance of ectomycorrhizal (ECM) fungi in forest ecosystems, knowledge about the ecological and co-evolutionary mechanisms underlying ECM host associations remains limited. Using a widely distributed group of ECM fungi known to form tight associations with trees in the family Pinaceae, we characterized host specificity among three unique Suillus–host species pairs using a combination of field root tip sampling and experimental bioassays. We demonstrate that the ECM fungus S. subaureus can successfully colonize Quercus hosts in both field and glasshouse settings, making this species unique in an otherwise Pinaceae-specific clade. Importantly, however, we found that the colonization of Quercus by S. subaureus required co-planting with a Pinaceae host. While our experimental results indicate that gymnosperms are required for the establishment of new S. subaureus colonies, Pineaceae hosts are locally absent at both our field sites. Given the historical presence of Pineaceae hosts before human alteration, it appears the current S. subaureus–Quercus associations represent carryover from past host presence. Collectively, our results suggest that patterns of ECM specificity should be viewed not only in light of current forest community composition, but also as a legacy effect of host community change over time.
Bibliographical noteFunding Information:
We thank D. McLaughlin for his documentation of the S. subaureus population at Lake Alexander SNA, Y. Han for assistance in processing the bioassays, G. Celio at the UNM Imaging Center for assistance with the Hartig net micrographs, and members of the Kennedy lab as well as three anonymous reviewers and F. Martin for constructive comments on previous versions of the manuscript. Financial support was provided by a National Science Foundation (NSF) Graduate Research Fellowship (grant no. 00039202) to L.L. and NSF DEB grant no. 1554375 to P.G.K.
- ectomycorrhizal (ECM) fungi
- host specificity
- legacy effects
- neighborhood effects