Microbial and isotopomer analysis of N2O production pathways in a calcareous film-mulched farmland

The effects of long-term film mulching and primary nitrogen (N) fertilization strategies on the microbial processes underlying N 2 O emissions from calcareous upland soils are poorly understood. A two-year field experiment including five treatments viz . no mulching with recommended N (N 225 ), film mulching with recommended N (F 225 ), high dose N (F 380 ), manure addition (F 225+M ), and no N (F 0 ) was conducted to explore the N 2 O production pathways in a maize ( Zea mays L.) cultivation system using combined isotopocule and quantitative PCR analysis. The cumulative N 2 O emissions were 0.56 − 0.68, 0.70 − 0.71, 1.06 − 1.07, 1.50 − 1.54, and 0.16 − 0.19 kg N 2 O-N ha −1 in N 225 , F 225 , F 380 , F 225+M and F 0 treatments, respectively. Nitrifier denitrification and/or classical denitrification accounted for 53.4 − 85.0% of the total N 2 O emissions in the high N 2 O emission period. Long-term film mulching changed the N 2 O-related community composition and led to a significantly higher fraction of bacterial denitrification and/or nitrifier denitrification (f denitrification ) in most events, compared with those in bare land. A relatively low f denitrification and high N 2 O/(N 2 O + N 2 ) ratio often occurred in the F 225+M (in mixing-reduction scenario) and F 380 treatments. Correlation analysis suggested that N 2 O fluxes were positively correlated with NO 3 − -N, dissolved organic N, total N, soil temperature, soil organic carbon, and the abundance of AOB amoA and nosZ genes, whereas they were negatively correlated with soil pH and C/N. Overall, our results suggest that long-term film mulching and N fertlization strategies could impact the processes of N 2 O production and consumption, whereas denitrification was still the primary N 2 O production pathways.