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

Abstract

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 ¹³C-labelled substrates (acetate, butyrate, glucose; 80 μg C g¯¹), with water as a control, and ¹⁵N-labelled N (300 μg 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 μmol 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 μmol m¯² s¯¹ and 10.9 ± 6.5 mg N m¯² h¯¹) or butyrate (0.61 ± 0.11 μmol 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 μmol C m¯² s¯¹) than that for glucose (0.02 ± 0.10 μmol C m¯² s¯¹), while butyrate addition resulted in negative priming (−0.09 ± 0.05 μmol 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.