Reproduction of most flowering plants depends on pollination by animals, corresponding to two thirds of our agricultural crops. In order to secure food production, it is necessary to improve our understanding of factors influencing plant fecundity and plant-pollinator interactions. Plant-pollinator interactions can be influenced not only by the diversity of the resident plant community or other aboveground organisms but also by belowground organisms. Here, we work in native tallgrass prairie communities to test if 1) increased plant diversity of the resident community increases the rate of pollinator visitation and thus indirectly influences plant fecundity; and if 2) plant-soil microbial interactions mediate plant-pollinator interactions and thus indirectly affect plant fecundity. To untangle direct and indirect effects of above- and belowground interactions that influence plant fecundity, we performed pollination manipulations and pollinator observations in experimental plant communities that varied in the number of plant species (1, 6 species) and in the composition of soil microbial communities (with, without live soil microbes).
Results/Conclusions
We found that Rudbeckia hirta experienced significantly higher pollinator visitation rates when grown in polycultures compared to monocultures, while there was no significant difference in visitation rates between plants grown in the presence or absence of live soil microbes. This suggests that for this species, diversity of the resident plant community might increase plant fecundity indirectly by changing pollinator behavior. However, R. hirta produced larger flowerheads when grown with live soil microbes and thus might inherently have higher fecundity in the presence of live soil microbes despite having no differences in pollinator visitation rates. Other species showed no significant difference in pollinator visitation between treatments, suggesting that pollinators are not mediating the effects of diversity or soil microbes in those species. We will connect our results to actual seed count data to determine if the observed differences in pollinator visitation rates result in changes in plant fecundity.