Abstract
A clear understanding of the effects of manure, biochar and nitrification inhibitors (NI, nitrapyrin-SNI and Sorghum bicolor L.-BNI) amendment on nitrous oxide (N2O) production pathways and consumption remains elusive under field conditions. A field experiment using an isotopocule mapping approach (δ15NSPN2O and δ18ON2O/H2O map) in conjunction with molecular techniques were conducted to understand the mechanisms of these options for N2O 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 N2O emission, but also stimulated N2O reduction to N2 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 N2O derived from nitrification and/or bacterial denitrification/nitrifier denitrification demonstrated from the simultaneous decrease of soil NO2− and NO3− and increase of soil NH4+ intensity together with the lower AOB amoA transcripts in NIs than in the urea. These results helped explain the observed differences in N2O emissions among these mitigation options, and laid the foundation for a better understanding of N2O production and reduction under field conditions.
Published Version
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