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 (N2O) emissions from soil are also linked to C substrate dynamics; however, the relationship between the priming effect and N2O 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 N2O emissions. We applied C-13-labelled substrates (acetate, butyrate, glucose; 80 pg C g(-1)), with water as a control, and 15N-labelled N (300 pg N g(-1) soil, potassium nitrate) to three different soils, and, after 3 days, we measured the effects on the priming of SOM and sources of N2O emission. Carbon substrate addition increased both CO2- and SOM-derived N2O emissions in the presence of exogenous N. Emissions of CO2 and N2O from soils with added glucose (mean +/- standard deviation, 0.73 +/- 0.13 mu mol m(-2) s(-1) and 21.4 +/- 12.1 mg N m(-2) h(-1)) were higher (p < 0.05) than those from soils treated with acetate (0.64 +/- 0.11 mu mol m(-2) s(-1) and 10.9 +/- 6.5 mg N m(-2) h(-1)) or butyrate (0.61 +/- 0.11 mu mol m(-2) s(-1) and 11.0 +/- 6.6 mg N m(-2) h(-1)), respectively. Acetate addition induced a stronger (p < 0.05) priming effect on soil C (0.07 +/- 0.09 mu mol C m(-2) s(-1)) than that for glucose (0.02 +/- 0.10 mu mol C m(-2) s(-1)), while butyrate addition resulted in negative priming (-0.09 +/- 0.05 mu mol C m(-2) s(-1)). SOM-derived N2O emissions were relatively low from soils with butyrate addition (1.4 +/- 1.5 mg N m(-2 )h(-1)) compared with acetate (2.9 +/- 2.3 mg N m(-2) h(-1)) or glucose (9.2 +/- 4.5 mg N m(-2) h(-1)). There was no clear relationship between the priming effect and SOM-derived N2O 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 N2O emissions.