Mechanisms of mitigating nitrous oxide emissions from vegetable soil varied with manure, biochar and nitrification inhibitors.

• Manure and biochar mitigated N 2 O emissions via dual effects on denitrification. • NIs mitigated N 2 O emissions via inhibiting both nitrification and denitrification. • BNI increased nirS , nosZⅠ and fungal nirK transcripts following fertilization. • The higher NO 3 − content led to a lower N 2 O reduction during denitrification. A clear understanding of the effects of manure, biochar and nitrification inhibitors (NI, nitrapyrin-SNI and Sorghum bicolor L.-BNI) amendment on nitrous oxide (N 2 O) production pathways and consumption remains elusive under field conditions. A field experiment using an isotopocule mapping approach (δ15NSP N2O and δ18O N2O/H2O map) in conjunction with molecular techniques were conducted to understand the mechanisms of these options for N 2 O mitigation in a Tung choy (Ipomoea aquatic Forssk.) vegetable soil. The manure substitution and biochar not only decreased nitrification/fungal denitrification and bacterial denitrification/nitrifier denitrification-derived N 2 O emission, but also stimulated N 2 O reduction to N 2 during the denitrification process as evidenced from the decrease of ammonia-oxidizing bacteria (AOB) amoA and the increase of nirS , nosZⅠ , nosZⅡ and fungal nirK transcripts. Biochar had a greater potential to enhance this reduction with decrease of ammonia-oxidizing archaea (AOA) amoA transcripts. NIs mitigated the N 2 O derived from nitrification and/or bacterial denitrification/nitrifier denitrification demonstrated from the simultaneous decrease of soil NO 2 − and NO 3 − and increase of soil NH 4 + intensity together with the lower AOB amoA transcripts in NIs than in the urea. These results helped explain the observed differences in N 2 O emissions among these mitigation options, and laid the foundation for a better understanding of N 2 O production and reduction under field conditions. [ABSTRACT FROM AUTHOR]