The Microbiology Behind Periodical Cicada-Induced Gas Pulses from Forest Soils

This study was conducted using the 2021 Brood X emergence of periodical cicadas in the United States of America (U.S.), which began in mid-May 2021, as a model for periodical cicada ecosystem disturbance. Cicadas were collected around Bloomington, Indiana (IN), U.S. The experimental site was located in mixed deciduous forest Griffy Woods in southern IN. Measurements of potential gas fluxes were made from 6 microcosms, with 2880 datapoints per sample. Analysis of microbial communities from field chambers was carried out on 20 samples. Analysis of microbial communities from the time series experiments was carried out on 64 samples. Measurements of respiration rates were made from 6 OxiTop® respirometers, with one datapoint per day. Quantification of nitrate and ammonification was carried out on 32 samples. Quantification of C:N was carried out on 15 samples. We found that the interface between cicada carcasses and soil surfaces is the site of enhanced microbial nutrient cycling that leads to a pulse of N2O and NH3 after ~10-15 days. The dominant mechanism of N2O and NH3 production is likely dissimilatory nitrate reduction to ammonia (DNRA), as indicated by increased abundance of DNRA taxa on cicada carcass surfaces (the necrobiome) synchronous with the gas pulses.