Hybridization in Populus alters the species composition and interactions of root-colonizing fungi: Consequences for host plant performance¹

Interactions among plants and soil microbes can significantly influence plant communities, yet we understand little about how hybridization of plant species might alter these interactions. In addition, few studies have explored the effects of different components of soil microbial communities on plant performance. We tested for feedbacks between soil microbes within a Populus hybridizing system using approaches that allowed us to isolate the effects of arbuscular mycorrhizal fungi (AMF) and root endophytes. We found significant differences among the arbuscular mycorrhizal (AM) fungal spore communities cultured from Populus angustifolia James, Populus fremontii S. Watson, and their F₁ hybrids. Populus angustifolia cuttings grew 40% larger when inoculated with AM fungal spores from F₁ hybrids than with spores from P. fremontii, while growth with spores from P. angustifolia was intermediate. However, parental and hybrid inocula promoted growth equally when soil inoculum was used. Roots inoculated with AM fungal spores alone were colonized principally by AMF, while those inoculated with soil were colonized mostly by dark septate endophytes. These results indicate that genetic variation among hybridizing plant species can influence both microbial communities and their interactions with host plants, but these effects depend upon the type of microbe. Furthermore, our results suggest that interactions among fungi during root colonization may alter the composition and function of the plant microbiome.