COS 252-4 - Periodical cicada effects on soil nitrogen cycling: Ecosystem consequences of a not-so-silent spring

Abstract: Periodical cicadas (Magicicada spp.) affect tree physiology, food abundance for insectivorous predators, and soil porosity, but their impacts on ecosystem nitrogen (N) cycling remain poorly quantified. We took advantage the Brood X emergence in 2021 to ask the following: How do periodical cicadas affect microbial N cycling, to what extent do changes vary over space and across time, and what are potential consequences of such effects for N retention and loss in forests? We conducted an observational study and an experimental study in the mixed hardwood forests of south-central Indiana to address these questions. In the observational study, we sampled soils adjacent to (and distant from) cicada emergence holes, and measured rates of N mineralization and nitrification, and gaseous efflux of N₂O (which depends on microbial nitrification and denitrification). In the experimental study, we compared N processes (soils and gaseous fluxes) in chambers and plots fertilized with cicada carcasses and compared these to unamended controls. In the observational study, we found no differences in N cycling between soils adjacent to emergence holes vs. soils distant from emergence holes (P > 0.05). These patterns were robust across multiple periods of the growing season and were unaffected by the dominant tree species present. In contrast, experimental addition of carcasses increased N cycling rates by 20-60% (P < 0.05), with the largest effects occurring in plots dominated by tree species that associate with ectomycorrhizal fungi. Moreover, while N₂O fluxes were unaffected by the presence/absence of emergence holes, N₂O fluxes were 3-5 fold greater in plots amended with cicada carcasses compared to controls (P < 0.05). Collectively, our results indicate that while periodical cicadas may have consequences for ecosystem N cycling in the emergence year, their effects on ecosystem-scale N retention and loss are likely minor and attenuated over time.