Chemical identity of carbon substrates drives differences in denitrification and N2O reduction within agricultural soils

Rates of nitrous oxide (N2O) production from agricultural soils are highly variable across space and time. Improving predictions of N2O emissions will require improving our understanding of the drivers of denitrification and the sources of variability in the rates of N2O production between soils and over time. While the amount of available carbon (C) is a known control on denitrification and N2O reduction, relatively little attention has been paid to the effect of the chemical identity of C substrates on rates of denitrification and N2O reduction. We investigated the effects of twelve different C-substrate additions on the production and reduction of N2O in five soils taken from two distinct agricultural locations in Michigan under multiple land uses. We provided additions of glucose, cellulose, N-acetyl-glucosamine, chitin, amino acids, protein, vanillyl alcohol, lignin, citrate, succinate, methanol, and water in laboratory denitrification potential assays to determine the effects of denitrifier C preference on denitrification rates. We found that amino acids, protein, and organic acids stimulated the greatest rates of denitrification potential across all land uses. Similarly, we found these same substrates caused the most N2O reduction, resulting in the lowest net concentrations of N2O. Soils from agricultural rotations without cover crops had overall lower rates of denitrifier activity, leading to less net N2O production compared to soils from other land uses. In general, C-utilization patterns were similar among all soils, and C-substrate identity had a much stronger effect than land use. Here, we demonstrate that the chemical identity of available C gives rise to wide variability in rates of denitrification and N2O reduction.