Abstract
Denitrification is a key biochemical process in nitrogen cycling and nitrous oxide (N2O) production. In this study, the impacts of different inorganic and organic amendments (OAs) on the abundance of denitrifying genes (nirS, nirK and nosZ) and the level of N2O emission were examined with incubation experiments. Six treatments included the indicated applications: (i) no fertilization (CK); (ii) urea application alone (U); (iii) wheat straw plus urea (U + WS); (iv) pig manure plus urea (U + PM); (v) compost product plus urea (U + CP); and (vi) improved compost product plus urea (U + IC). The results indicated that all fertilization treatments increased accumulative N2O emissions compared with the CK treatment. The U + WS, U + PM and U + CP treatments increased N2O emissions by 2.12–141.3%, and the U + IC treatment decreased N2O emissions by 23.24% relative to the U treatment. nirK was the dominant denitrification gene rather than nirS and nosZ found in soil. Additionally, the highest abundance of nirK gene was that with the U + PM treatment, and the lowest was that with the U + IC treatment. Additionally, changes in the nirK gene were highly correlated with levels of dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and nitrate nitrogen (NO3–N). Automatic linear modeling revealed that N2O emission was closely related to the nirK gene, DOC and NO3–N. Overall, the use of urea and improved compost as co-amendments retarded N2O emission to a considerable degree compared with other OA additions.
Highlights
Denitrification is a key biochemical process in nitrogen cycling and nitrous oxide (N2O) production
N 2O emissions peaked on day 3 for the CK, U, U + wheat straw (WS) and U + pig manure (PM) treatments and peaked on day 4 for the U + improved-compost product (IC) and U + compost product (CP) treatments
The maximum peak value for N 2O emissions among all organic amendments (OAs) was that seen with the U + PM treatment (76.04 mg/kg/day), and the minimum value of N2O emissions was that seen with the U + IC treatment (21.44 mg/kg/day)
Summary
Denitrification is a key biochemical process in nitrogen cycling and nitrous oxide (N2O) production. The impacts of different inorganic and organic amendments (OAs) on the abundance of denitrifying genes (nirS, nirK and nosZ) and the level of N2O emission were examined with incubation experiments. The abundance of nirS, nirK and nosZ denitrifying genes was used to study soil nitrogen cycling and N 2O emissions[10,11]. Hai et al.[22] found that organic fertilizers increased the abundance of nirS and nirK genes and enhanced N2O emissions. Huang et al.[23] reported that co-addition of urea and cattle manure decreased the abundance of nirS and nirK but increased N 2O emissions. Xu et al.[24] suggested that nirS-type denitrifying genes showed strong correlations with significant increases in N2O emissions from soils undergoing organic fertilization. There was still a knowledge gap regarding the dominant drivers of N 2O emissions, including denitrifiers and environmental factors
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