Using isotope pool dilution to understand how organic carbon additions affect N2O consumption in diverse soils

Nitrous oxide (N₂O) is a formidable greenhouse gas with a warming potential ~300× greater than CO₂. However, its emissions to the atmosphere have gone largely unchecked because the microbial and environmental controls governing N₂O emissions have proven difficult to manage. The microbial process N₂O consumption is the only know biotic pathway to remove N₂O from soil pores and therefore reduce N₂O emissions. Consequently, manipulating soils to increase N₂O consumption by organic carbon (OC) additions has steadily gained interest. However, the response of N₂O emissions to different OC additions are inconsistent, and it is unclear if lower N₂O emissions are due to increased consumption, decreased production, or both. Simplified and systematic studies are needed to evaluate the efficacy of different OC additions on N₂O consumption. We aimed to manipulate N₂O consumption by amending soils with OC compounds (succinate, acetate, propionate) more directly available to denitrifiers. We hypothesized that N₂O consumption is OC‐limited and predicted these denitrifier‐targeted additions would lead to enhanced N₂O consumption and increased nosZ gene abundance. We incubated diverse soils in the laboratory and performed a ¹⁵N₂O isotope pool dilution assay to disentangle microbial N₂O emissions from consumption using laser‐based spectroscopy. We found that amending soils with OC increased gross N₂O consumption in six of eight soils tested. Furthermore, three of eight soils showed Increased N₂O Consumption and Decreased N₂O Emissions (ICDE), a phenomenon we introduce in this study as an N₂O management ideal. All three ICDE soils had low soil OC content, suggesting ICDE is a response to relaxed C‐limitation wherein C additions promote soil anoxia, consequently stimulating the reduction of N₂O via denitrification. We suggest, generally, OC additions to low OC soils will reduce N₂O emissions via ICDE. Future studies should prioritize methodical assessment of different, specific, OC‐additions to determine which additions show ICDE in different soils.