Plant-soil feedbacks, soil microbial inoculations, and restoration of native diversity
Plant interactions with soil microbial communities can increase plant species diversity and maintain ecosystem function. Given the importance of these interactions, there have been several calls to better incorporate soil microbial communities into the practice of ecological restoration. Beyond their potential to increase diversity and function in restored ecosystems, it is also possible that plant-microbial interactions act as drivers of secondary succession. If so, understanding these interactions will allow us to better predict the successional trajectories of restored ecosystems and to develop innovations in restoration practice that will accelerate the recovery of disturbed ecosystems. Here, we report results from a series of experiments in the tallgrass prairie testing the associations between a plant species’ life history and that species’ interactions with soil microbial communities. First, we test how plant-soil feedbacks vary between species representing a gradient of life histories, from early to late successional. We follow this experiment with a test of the association between a plant species’ life history and that species’ dependence on mycorrhizal fungi. To determine the relevance of these results to ecological restoration, we experimentally inoculated an abandoned agricultural field with either whole soil or mycorrhizal fungi isolated from undisturbed remnant prairies and monitored the relative success of early and late-successional plant species in inoculated plots and un-inoculated controls.
In tests of plant-soil feedbacks, we found that early successional plant species experienced stronger negative feedbacks than late successional plant species, as indicated by a significant correlation between a species’ successional association and the plant-soil feedbacks these species experienced (r2 = 0.78, p = 0.02). We also found that dependence on mycorrhizal fungi is associated with a plant species’ life history. Early successional plant species grew more quickly overall (F3,21=8.0, p=0.0009), but late successional plant species were more responsive to inoculation with mycorrhizal fungi than early successional plants (F1,21=12.1, p=0.002). In our field inoculation experiments both whole soil and mycorrhizal inocula improved the growth and survivorship of many prairie plant species, with late successional plant species showing the strongest responses to inoculation with whole soil from undisturbed remnant prairies. Overall, our results indicate that plant interactions with soil microbial communities are an important component of the life-history trade-offs that underlie shifts in species abundance during succession. By understanding these interactions, we gain an improved ability to predict the trajectories of ecological restorations and to develop interventions that consistently re-establish late successional plant communities.