Using isotope pool dilution to understand how organic carbon additions affect N<sub>2</sub>O consumption in diverse soils
Emily R. Stuchiner, Joseph C. von Fischer
Abstract
Abstract 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 I ncreased N 2 O C onsumption and D ecreased N 2 O E missions (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.