Production and consumption of N2O during denitrification in subtropical soils of China

Nitrous oxide (N2O) production and reduction rates are dependent on the interactions with each other and it is therefore important to evaluate them within the context of simultaneously operating N2O emission and reduction. The objective of this study was to quantify the simultaneously occurring N2O emission and reduction across a range of subtropical soils in China, to gain a mechanistic understanding of potential N2O dynamics under the denitrification condition and their important drivers, and to evaluate the potential role of the subtropical soils as either sources or sinks of N2O through denitrification. Soils (45, from a range of different land uses and soil parent materials) were collected from the subtropical region of Jiangxi Province, China, and tested for their potential capacity for N2O emission and N2O reduction to N-2 during denitrification. N2O emission and reduction were determined in a closed system under N-2 headspace after the soils were treated with 200 mg kg(-1) NO (3) (-) -N and incubation at 30 A degrees C for 28 days. The soil physical and chemical properties, the temporal variations in headspace N2O concentration, and NO (3) (-) -N and NH (4) (+) -N concentrations in the soil slurry were measured. Variations in N2O concentration (N) over incubation time (t) were consistent with an equation in which average R (2) = 0.84 +/- 0.11 (p < 0.05): , where A is the total N2O emission during the incubation, B is a constant, and k (1) and k (2) are the N2O emission constant and reduction constants, respectively. The results of the simulation showed that k (1) was greater than k (2). The reduced amount of NO (3) (-) -N in the first 7 days of incubation and the N2O emission rate (the percentage of A value relative to the amount of NO (3) (-) -N reduced during the 28-day incubation, R (n)) were able to explain 82.9 % (p < 0.01) of the variation in total N2O emission (A) during the incubation for the soil samples studied, indicating that the total amount of N2O emitted was determined predominately by denitrification capacity. Soil organic carbon content and soil nitrogen mineralization are the key factors that determine differences in the amounts of reduced NO (3) (-) -N among the soil samples. The R (n) value decreased with increasing k (2) (p < 0.01), indicating that soils with higher N2O reduction capacity under these incubation conditions would emit less N2O per unit of denitrified NO (3) (-) -N than the other soils. Results are valuable in the evaluation of net N2O emissions in the subtropical soils and the global N budget. In a closed, anaerobic system, variations in N2O concentration in the headspace over the incubation time were found to be compatible with a nonlinear equation. Soil organic carbon and the amount of NH (4) (+) -N mineralized from the organic N during the first 7 days of incubation are the key factors that determine differences in the N2O emission constant (k (1)), the N2O reduction constant (k (2)), the total N2O emission during the incubation (A) and the N2O emission rate (R (n)).