Emissions of nitrous oxide, dinitrogen and carbon dioxide from three soils amended with carbon substrates under varying soil matric potentials

Carbon (C) substrates are critical for regulating denitrification, a process that results in nitrous oxide (N 2 O) and dinitrogen (N 2 ) emissions from soil. However, the impacts of C substrates on concomitant soil emissions of carbon dioxide (CO 2 ) and N 2 O under varying soil types and soil water contents are not well studied. Three repacked Pallic grassland soils, varying in texture and phosphorus (P) status, containing NO 3 − ‐ 15 N were held at three levels of matric potential ( ψ , −3, −5 and −7 kPa), while receiving daily substrate additions (acetate, glucose and water control) for 14 days. The CO 2 and N 2 O emissions were measured daily. Additionally, the N 2 O:(N 2  + N 2 O) ratios were determined using 15 N on days 3 and 14. Results showed that N 2 O emissions increased exponentially as soil gas diffusivity declined, and N 2 O peak emissions were higher with glucose than with acetate addition, with a range (± standard deviation) of 0.1 ± 0.0 to 42.7 ± 2.1 mg N m −2  h −1 . The highest cumulative N 2 O emission (2.5 ± 0.2 g N m −2 ) was measured following glucose addition with a soil ψ of −3 kPa. In comparison with added glucose, acetate resulted in a twofold increase in N 2 emissions in soils with relatively low gas diffusivities. The N 2 O:(N 2 O + N 2 ) emissions ratios varied with substrate (glucose, 0.91; acetate, 0.81) on day 3, and had declined by day 14 under substrate addition (≤0.10). Cumulative CO 2 emissions were enhanced with increasing soil gas diffusivity and were higher for soils amended with glucose (ranging from 22.5 ± 1.3 to 36.6 ± 1.8, g C m −2 ) than for those amended with acetate. Collectively, the results demonstrate that the increase of N 2 O, N 2 and CO 2 emissions and changes in the N 2 O:(N 2  + N 2 O) ratio vary over time in response to C substrate type and soil gas diffusivity. Highlights Co‐regulation of CO 2 and N 2 O emissions was assessed for varying soil types and C substrates. Soil diffusivity explained concurrently cumulative N 2 O and CO 2 emissions. Acetate enhanced N 2 O reduction to N 2 in three grassland soils more than glucose. C substrate effects on soil N 2 O, N 2 and CO 2 emissions were soil type specific.