PS 11-147 - Local extinction in plant communities may lead to increased invasion success through soil microbial changes

Abstract: Biodiversity loss can lead to a variety of changes in ecosystems, though in many cases the mechanisms of how species declines create these outcomes are unknown. For example, realistic patterns of local plant species extinction in the California grasslands have been shown to lead to increases in species invasions, particularly by Centaurea solstitialis (yellow starthistle). Notably, the effects of species loss in this system are driven by local extinction of rare species, begging the question of how the presence or absence of species at low abundance could have such disproportionate impacts on communities. Soil microbial communities might respond disproportionately to changes in plant community composition and are known to strongly affect the growth of plants, including C. solstitialis. Here we examine the potential for soil microbial communities to be mediating the effects of plant biodiversity loss in this system. Specifically, we ask if the soil microbiome changes as a result of realistic species loss, and if such changes affect invasive C. solstitialis growth and productivity. To address this question, we utilized soils from a three year field experiment that manipulated plant species richness according to both random and realistic combinations of species. We used the microbial communities from those soils as inoculum to grow C. solstitialis for eight weeks and tested for differences in growth rate and above- and below-ground biomass allocation. We predicted that lower plant community diversity and its associated microbial community would lead to an increase in the growth rate of C. solstitialis. We found that the leaves of C. solstitialis grew faster under inocula from lower realistic plant diversity as compared to the randomized plant loss control, but found no difference in biomass allocation between treatments. This indicates a potential relationship between aboveground biodiversity loss and the successful invasion of C. solstitialis. Our results suggest that the soil microbiome may mediate disproportionate effects of species loss on plant communities and constitute an important mechanism for the impacts of biodiversity loss on ecosystems.