Using isotope pool dilution to understand how organic carbon additions affect N(2)O consumption in diverse soils

Nitrous oxide (N(2)O) is a formidable greenhouse gas with a warming potential ~300× greater than CO(2). However, its emissions to the atmosphere have gone largely unchecked because the microbial and environmental controls governing N(2)O emissions have proven difficult to manage. The microbial process N(2)O consumption is the only know biotic pathway to remove N(2)O from soil pores and therefore reduce N(2)O emissions. Consequently, manipulating soils to increase N(2)O consumption by organic carbon (OC) additions has steadily gained interest. However, the response of N(2)O emissions to different OC additions are inconsistent, and it is unclear if lower N(2)O 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 N(2)O consumption. We aimed to manipulate N(2)O consumption by amending soils with OC compounds (succinate, acetate, propionate) more directly available to denitrifiers. We hypothesized that N(2)O consumption is OC‐limited and predicted these denitrifier‐targeted additions would lead to enhanced N(2)O consumption and increased nosZ gene abundance. We incubated diverse soils in the laboratory and performed a (15)N(2)O isotope pool dilution assay to disentangle microbial N(2)O emissions from consumption using laser‐based spectroscopy. We found that amending soils with OC increased gross N(2)O consumption in six of eight soils tested. Furthermore, three of eight soils showed Increased N(2)O Consumption and Decreased N(2)O Emissions (ICDE), a phenomenon we introduce in this study as an N(2)O 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 N(2)O via denitrification. We suggest, generally, OC additions to low OC soils will reduce N(2)O emissions via ICDE. Future studies should prioritize methodical assessment of different, specific, OC‐additions to determine which additions show ICDE in different soils.