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 N₂O emissions from calcareous upland soils are poorly understood. A two-year field experiment including five treatments viz. no mulching with recommended N (N₂₂₅), film mulching with recommended N (F₂₂₅), high dose N (F₃₈₀), manure addition (F_225+M), and no N (F₀) was conducted to explore the N₂O production pathways in a maize (Zea mays L.) cultivation system using combined isotopocule and quantitative PCR analysis. The cumulative N₂O emissions were 0.56 − 0.68, 0.70 − 0.71, 1.06 − 1.07, 1.50 − 1.54, and 0.16 − 0.19 kg N₂O-N ha⁻¹ in N₂₂₅, F₂₂₅, F₃₈₀, F_225+M and F₀ treatments, respectively. Nitrifier denitrification and/or classical denitrification accounted for 53.4 − 85.0% of the total N₂O emissions in the high N₂O emission period. Long-term film mulching changed the N₂O-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 N₂O/(N₂O + N₂) ratio often occurred in the F_225+M (in mixing-reduction scenario) and F₃₈₀ treatments. Correlation analysis suggested that N₂O fluxes were positively correlated with NO₃⁻-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 N₂O production and consumption, whereas denitrification was still the primary N₂O production pathways. [ABSTRACT FROM AUTHOR]