The plant-soil feedback framework has been used to simplify the complexity of plant-rhizosphere interactions. For example, one prediction of the framework is that host-specific interactions between plants and soil microorganisms can lead to negative density dependence, which stabilizes the coexistence of competing plant species. We present a novel application of the plant-soil feedback framework to the microbial communities of aboveground tissues, hereafter termed “plant-phyllosphere feedback”. Specifically, we measured plant growth responses to the presence of microbial communities from the previous season’s leaf litter and current mature leaves of conspecific and heterospecific plants from four herbaceous plant species (Aster novae-angliae, Cacalia atriplicifolia, Eupatorium perfoliatum, Vernonia missurica). We established an additional experiment in order to compare rhizosphere-mediated soil feedback amongst the same four species, as well as to simultaneously compare the direction and magnitude of feedback effects generated by rhizosphere vs. phyllosphere inocula sources. Each experiment was performed under controlled greenhouse conditions. Soil and leaf inocula sources were derived from mature field plants grown in a common garden. Lastly, we performed a third experiment in the field, using the same plant-soil feedback framework, in order to test the combined effects of plant-soil feedback, plant-phyllosphere feedback, and plant interspecific competition.
Results/Conclusions
Overall, we found significant net overall plant-phyllosphere feedback, validating the utility of the plant-soil feedback framework for the study of microbial communities in phyllosphere tissues. Initially, we found that all four plant species experienced individual negative feedback in seedling size when inoculated with leaf litter, which was the first inocula source in the plant-phyllosphere experiment. Following a further 12 weeks of growth and exposure to the second leaf inocula source (mature leaves) all four species still showed negative plant-phyllosphere feedback, but this was significant only for C. atriplicifolia and E. perfoliatum. Similarly, three of the four species experienced negative plant-soil feedback except for C. atriplicifolia, which showed positive plant-soil feedback. Using the plant-soil feedback framework, we also found significant net overall feedback on aboveground biomass in the field experiment. Field-based feedback for the four species were each individually negative, though variable in magnitude between species. Our results suggest that both rhizosphere and phyllosphere microbial communities have the potential to mediate plant species coexistence and plant population dynamics, and that extension of the plant-soil feedback framework to phyllosphere-associated microbial communities is a valuable approach for understanding these complex species interactions.