The plant-soil feedback framework has provided an effective model for understanding plant interactions with belowground microbiota. Aboveground microbiota may have similarly important effects on plant health and the coexistence of competing plant species, so there is potential to incorporate aboveground microbiota into the frameworks developed for plant-soil interactions. Aboveground microbial communities can colonize plant seedlings via persistent leaf litter, which may affect young plants as they come into contact with con- or heterospecific leaf litter from neighboring plants. In this experiment, we investigated how seedling establishment is affected by con- and heterospecific litter microbiota. Using a full-factorial experimental design, ten native Asteraceae species that varied in life history and phylogenetic relatedness were grown under controlled greenhouse conditions for four weeks before exposure to con- or heterospecific leaf litter. Plant litter from the ten species was collected from mature plants growing in a common garden. Each individual plant was isolated in a humidity chamber to prevent cross contamination among treatments. After three weeks of exposure, seedlings were harvested and measured for plant biomass as a metric of seedling fitness.
Using the statistical framework developed for studies of plant-soil interactions, average pairwise feedback was calculated for each species. We found that four out of the ten species experienced reduced growth when exposed to their own leaf litter (i.e., conspecific) than when exposed to leaf litter from different species (i,e., heterospecific). An additional three species experienced marginally significant negative plant litter feedback. These findings indicate that negative feedbacks can arise through plant species interactions with aboveground microbiota, and these interactions have the potential to stabilize species coexistence. Many microbial pathogens tend to be host specific. Following this line of reasoning, microbial sources from plant litter may decrease fitness when litter is conspecific rather than heterospecific. These negative feedback effects could also be key factors in spatial patterns of seedling establishment and mimic results from previous plant-soil feedback studies. In a larger ecological context, litter microbiota may be an underappreciated mechanism driving plant community diversity in natural systems.