The effect of temperature and moisture on the source of N2O and contributions from ammonia oxidizers in an agricultural soil

In recent years, identification of the microbial sources responsible for soil N2O production has substantially advanced with the development of isotope enrichment techniques, selective inhibitors, mathematical models and the discoveries of specific N-cycling functional genes. However, little information is available to effectively quantify the N2O produced from different microbial pathways (e.g. nitrification and denitrification). Here, a N-15-tracing incubation experiment was conducted under controlled laboratory conditions (50, 70 and 85% water-filled pore space (WFPS) at 25 and 35 A degrees C). Nitrification was the main contributor to N2O production. At 50, 70 and 85% WFPS, nitrification contributed 87, 80 and 53% of total N2O production, respectively, at 25 A degrees C, and 86, 74 and 33% at 35 A degrees C. The proportion of nitrified N as N2O (P (N2O)) increased with temperature and moisture, except for 85% WFPS, when P (N2O) was lower at 35 A degrees C than at 25 A degrees C. Ammonia-oxidizing archaea (AOA) were the dominant ammonia oxidizers, but both AOA and ammonia-oxidizing bacteria (AOB) were related to N2O emitted from nitrification. AOA and AOB abundance was significantly influenced by soil moisture, more so than temperature, and decreased with increasing moisture content. These findings can be used to develop better models for simulating N2O from nitrification to inform soil management practises for improving N use efficiency.