Host-specific soil microbes contribute to habitat restriction of closely
related oaks (Quercus spp.)
Abstract
Habitat divergence among close relatives is a common theme in ecology.
While recent studies have frequently found that the abundance and
diversity of plant species are regulated by soil microbes, little is
known whether soil microbes can also affect the habitat distributions of
plants. To fill in this knowledge gap, we investigated whether
interactions with soil microbes restrict habitat distributions of
closely related oaks (Quercus spp.) in eastern North America. We
performed a soil inoculum experiment using two pairs of sister species
that show habitat divergence: Quercus alba (local species) vs. Q.
michauxii (foreign), and Q. shumardii (local) vs. Q. acerifolia
(foreign). To test whether host-specific soil microbes are responsible
for habitat restriction, we investigated the impact of local sister live
soil (containing soil microbes associated with local sister species) on
the survival and growth of local and foreign species. Secondly, to test
whether habitat-specific soil microbes are responsible for habitat
restriction, we also examined the effect of local habitat live soil
(containing soil microbes within local sister’s habitats, but not
directly associated with roots of local sister species) on the seedlings
of local and foreign species. We found that local sister live soil
decreased the survival and biomass of foreign species’ seedlings while
increased those of local species, which supports the roles of
host-specific microbes in mediating habitat exclusion. In contrast,
local habitat live soil did not differentially affect the survival or
biomass of the local vs. foreign sister species, providing no support
for the roles of habitat-specific microbes. Our study indicates that
soil microbes associated with one sister species can suppress the
recruitment of the other host species, contributing to habitat
partitioning of the closely related oaks. Our findings emphasize that
considering the complex interactions with soil microbes is essential for
understanding habitat distributions of closely related plants.