Associate Professor of Biology Indiana University, United States
Abstract: The emergence and subsequent death of periodical cicadas causes a pulse of nutrients, including nitrogen, into soils. Nutrient enrichment has immediate direct effects on plant growth but may also have more lasting intergenerational impact via maternal effects and changes in soil microbes. For example, increased resource availability is expected to contribute to maternal effects via seed provisioning, and nitrogen enrichment is predicted to reduce the importance of mutualistic interactions between legume plants and rhizobium bacteria. We capitalized on the summer 2021 emergence of 17-year Brood X periodical cicadas (Magicicada spp.) and performed a manipulative field experiment adding or removing cicada carcasses from forested plots to study the effect of cicada litterfall on plant and microbial communities. We hypothesized that cicada carcass addition would increase plant growth and survival via maternal effects but decrease the plant growth benefits of soil microbes. To test this, we collected hog peanut (Amphicarpaea bracteata) seeds from each plot, planted them in the greenhouse, and inoculated them in a factorial design with soil microbial communities from the addition and removal plots. Cicada addition affected early plant growth through both maternal effects and soil microbes but didn’t have lasting impacts on growth or fitness: seeds collected from cicada addition plots had a higher germination rate (p = 0.001) and soil microbes from cicada addition plots accelerated early plant development (days to form first true leaf, p = 0.034), but plant biomass, seed production, and root-shoot ratio were not significantly affected by seed or inoculate source. We also didn’t find any evidence for changes in mutualistic interactions between plants and rhizobia: nodule prevalence, abundance, and weight did not vary between cicada treatments. Overall, this study suggests that the nutrient pulse created by cicada litterfall affects plant growth via multiple mechanisms, including maternal effects and changes in soil microbial communities, but these intergenerational mechanisms are unlikely to have lasting effects on plant fitness.
