Abstract
Although ectomycorrhizal fungi have well-recognized effects on ecological processes ranging from plant community dynamics to carbon cycling rates, it is unclear if plants are able to actively influence the structure of these fungal communities. To address this knowledge gap, we performed two complementary experiments to determine (1) whether ectomycorrhizal plants can discriminate among potential fungal partners, and (2) to what extent the plants might reward better mutualists. In experiment 1, split-root Larix occidentalis seedlings were inoculated with spores from three Suillus species (S. clintonianus, S. grisellus, and S. spectabilis). In experiment 2, we manipulated the symbiotic quality of Suillus brevipes isolates on split-root Pinus muricata seedlings by changing the nitrogen resources available, and used carbon-13 labeling to track host investment in fungi. In experiment 1, we found that hosts can discriminate in multi-species settings. The split-root seedlings inhibited colonization by S. spectabilis whenever another fungus was available, despite similar benefits from all three fungi. In experiment 2, we found that roots and fungi with greater nitrogen supplies received more plant carbon. Our results suggest that plants may be able to regulate this symbiosis at a relatively fine scale, and that this regulation can be integrated across spatially separated portions of a root system.
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Acknowledgements
We thank Nhu Nguyen for collecting and logistical assistance with experiment 1. We thank Ford Denison, Tad Fukami, members of the Peay lab, Thomas Kuyper, and four anonymous reviewers for feedback on prior versions of this manuscript. Thanks also to Don Herman, who provided essential assistance with the isotope enrichment part of experiment 2.
Funding
S. Hortal received a Hawkesbury Institute for the Environment Research Exchange Program grant. L. Bogar received support for this research from a National Science Foundation (NSF) Graduate Research Fellowship Program grant, scholarships from the Mycological Society of San Francisco and the Phi Beta Kappa Northern California Association, and a predoctoral fellowship from the Stanford Center for Computational, Evolutionary, and Human Genomics. Further support was provided by an NSF-Division of Environmental Biology grant (1554375) to P. Kennedy.
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P.K. designed experiment 1, which was conducted by S.H. and J.H. L.B. designed and carried out experiment 2 with support from K.P. and A.K. L.B. analyzed the data and composed the manuscript, with writing and editing assistance from P.K., and additional revisions from all co-authors.
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Bogar, L., Peay, K., Kornfeld, A. et al. Plant-mediated partner discrimination in ectomycorrhizal mutualisms. Mycorrhiza 29, 97–111 (2019). https://doi.org/10.1007/s00572-018-00879-7
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DOI: https://doi.org/10.1007/s00572-018-00879-7