The soil in the U.S. Corn Belt is a net source of carbon dioxide and nitrous oxide and a weak sink for methane. Climate change is increasing the frequency and intensity of spring precipitation in this region resulting in intermittent ponding events, potentially changing soil biogeochemistry and the fluxes of greenhouse gases (GHGs) between soil and atmosphere. We measured trace gas fluxes, microbial community composition, and soil chemistry in response to experimental flooding events. We installed three treatments of collars—control, continuously flooded, and intermittently flooded—into bare ground in a central Illinois agricultural field. A drip irrigation system flooded the collar headspaces. The continuously flooded collars were inundated for the duration of the experiment (30 days), and the intermittently flooded collars were inundated for 72 hours per event and then kept dry for at least 5 days before the next flooding event. We measured N2O, CH4, and CO2 flux in situ using a static chamber connected to a cavity ringdown spectrometer. Nitrate, iron, and ammonium concentrations in soil were measured at intervals, and the identity and function of the soil microbial community was determined with cDNA and gene transcripts for methanogenesis, ammonification, and denitrification.
Results/Conclusions
We found that the soil microbial community was resilient to flooding and drying cycles, responded rapidly to changes in soil conditions, and that even low abundance taxa, such as methanogens (<0.01% of OTUs), were important drivers of net GHG fluxes. Iron oxidation states over the course of the experiment confirmed that flooding drove the soil into a reduced state. Integrating GHG fluxes across the period of the experiment, the intermittently flooded collars showed 89% higher global-warming potential of GHG fluxes at the 100-year horizon versus control, with most of change driven by increased net CO2 flux (87% higher) and net methane flux (29 times higher). These data indicate that more frequent flooding events can significantly increase net soil GHG emissions from the U.S. Corn Belt.