Genetic diversity and species diversity are typically studied in
isolation despite theory showing they likely influence one another.
Here, we used simplified communities of one or two populations of one or
two species to test whether linkages between genetic and species
diversity can be mediated by interactions between plants and their soil
microbiota, or microbe-mediated plant-soil feedback (PSF). Interspecific
PSF promotes the maintenance of species diversity when plants grow
better with heterospecific soil microbes than with conspecific microbes.
Similarly, intraspecific PSF promotes the maintenance of genetic
diversity when plants grow better with heterogenotypic than with
congenotypic microbes. We found that genetic diversity reduced the
ability of interspecific PSF to maintain species diversity, and, for one
study species, species diversity reduced the ability of intraspecific
PSF to maintain genetic diversity. If these patterns occur in more
diverse communities, then PSF may cause genetic and species diversity to
negatively influence one another.