Emissions of nitrous oxide, dinitrogen and carbon dioxide from three soils amended with carbon substrates under varying soil matric potentials
Yuan Li, Timothy J. Clough, Gabriel Y.K. Moinet, David Whitehead
Abstract
Abstract 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.