Response of N 2 O emission and denitrification genes to different inorganic and organic amendments

Denitrification is a key biochemical process in nitrogen cycling and nitrous oxide (N 2 O) 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 N 2 O 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 N 2 O emissions compared with the CK treatment. The U + WS, U + PM and U + CP treatments increased N 2 O emissions by 2.12–141.3%, and the U + IC treatment decreased N 2 O 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 (NO 3 – N). Automatic linear modeling revealed that N 2 O emission was closely related to the nirK gene, DOC and NO 3 – N. Overall, the use of urea and improved compost as co-amendments retarded N 2 O emission to a considerable degree compared with other OA additions.