Response of NO emission and denitrification genes to different inorganic and organic amendments.

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