Rapid climate change imperils many small-ranged endemic species as the climate envelopes of their native ranges shift poleward. In addition to abiotic changes, biotic interactions are expected to play a critical role in plant species’ responses. Below-ground interactions are of particular interest given increasing evidence of microbial effects on plant performance and the prevalence of mycorrhizal mutualisms. We used greenhouse mesocosm experiments to investigate how natural northward migration/assisted colonization of Rhododendron catawbiense, a small-ranged endemic eastern U.S. shrub, might be influenced by novel below-ground biotic interactions from soils north of its native range, particularly with ericoid mycorrhizal fungi (ERM). We compared germination, leaf size, survival, and ERM colonization rates of endemic R. catawbiense and widespread R. maximum when sown on different soil inoculum treatments: a sterilized control; a non-ERM biotic control; ERM communities from northern R. maximum populations; and ERM communities collected from the native range of R. catawbiense. Germination rates for both species when inoculated with congeners' novel soils were significantly higher than when inoculated with conspecific soils, or non-mycorrhizal controls. Mortality rates were unaffected by treatment, suggesting that the unexpected reciprocal effect of each species’ increased establishment in association with heterospecific ERM could have lasting demographic effects. Our results suggest that seedling establishment of R. catawbiense in northern regions outside its native range could be facilitated by the presence of extant congeners like R. maximum and their associated soil microbiota. These findings have direct relevance to the potential for successful poleward migration or future assisted colonization efforts.
Bibliographical noteFunding Information:
We thank the E.B. Horner Fellowship Fund for supporting T.M. and E.K. in their work on this project, and the Smith College Tomlinson Fund for providing funds for material costs. We thank S. Kapur, X. Liu and S. Chiu for their assistance with mesocosm maintenance and data collection. The New Hampshire Natural Heritage Bureau provided access to our study site in New Hampshire. We thank J. Wopereis and the Smith College Center for Microscopy for their support and facilitation of SEM microscopy, as well as the Moeller Lab for their comments on the manuscript. We also thank Bethany Bradley for providing county-level climate data.
© 2021, The Author(s).
- Assisted migration
- Biotic interactions
- Mycorrhizal mutualisms
- Plant-soil feedbacks
- Seedling establishment