Organic matter contributions to nitrous oxide emissions following nitrate addition are not proportional to substrate-induced soil carbon priming.

The addition of carbon (C) substrate often modifies the rate of soil organic matter (SOM) decomposition. This is known as the priming effect. Nitrous oxide (NO) emissions from soil are also linked to C substrate dynamics; however, the relationship between the priming effect and NO emissions from soil is not understood. This study aimed to investigate the effects of C and N substrate addition on the linkages between SOM priming and NO emissions. We applied C-labelled substrates (acetate, butyrate, glucose; 80 μg C g), with water as a control, and N-labelled N (300 μg N g soil, potassium nitrate) to three different soils, and, after 3 days, we measured the effects on the priming of SOM and sources of NO emission. Carbon substrate addition increased both CO- and SOM-derived NO emissions in the presence of exogenous N. Emissions of CO and NO from soils with added glucose (mean ± standard deviation, 0.73 ± 0.13 μmol m s and 21.4 ± 12.1 mg N m h) were higher (p < 0.05) than those from soils treated with acetate (0.64 ± 0.11 μmol m s and 10.9 ± 6.5 mg N m h) or butyrate (0.61 ± 0.11 μmol m s and 11.0 ± 6.6 mg N m h), respectively. Acetate addition induced a stronger (p < 0.05) priming effect on soil C (0.07 ± 0.09 μmol C m s) than that for glucose (0.02 ± 0.10 μmol C m s), while butyrate addition resulted in negative priming (-0.09 ± 0.05 μmol C m s). SOM-derived NO emissions were relatively low from soils with butyrate addition (1.4 ± 1.5 mg N m h) compared with acetate (2.9 ± 2.3 mg N m h) or glucose (9.2 ± 4.5 mg N m h). There was no clear relationship between the priming effect and SOM-derived NO emissions. The observed priming effect related to the potential electron donor supply of the C substrates was not observed. There is a need to further examine the role of soil priming in relation to soil NO emissions.