Linking genetic diversity and species diversity through plant-soil feedback

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.
In a two-generation greenhouse experiment, we conditioned the soil
microbial community with pairs of plants that were either two individuals
of the same species (lower species diversity) or one individual of each of
two species (higher species diversity), and with pairs of plants that were
either two individuals from the same population (lower genetic diversity)
or one individual from each of two populations (higher genetic diversity).
We then tested the effects of these microbial communities on plant growth
in a second generation. We found that higher genetic diversity reduced the
ability of interspecific PSF to promote plant species diversity, and for
one of our two study species, higher species diversity reduced the ability
of intraspecific PSF to promote plant genetic diversity. If these patterns
occur in more diverse communities, then our results suggest that PSF may
dampen the negative effects of diversity loss by promoting diversity at
other levels of biological organization.