Effect of Soil Moisture and Temperature on the Contribution of N2O Sources and Ammonia Oxidizer Growth in a Cropping Soil.

The continuous increase of the greenhouse gas nitrous oxide (N₂O) in the atmosphere due to increasing anthropogenic nitrogen input in agriculture has become a global concern. In recent years, identification of the microbial sources responsible for soil N₂O production has substantially advanced with the development of isotope enrichment and inhibition technologies and the discoveries of specific functional genes. However, little information is available to effectively quantify the N₂O sources. Therefore it is necessary to improve the understanding of N₂O formation and quantify the contribution of different pathways. To investigate this a ¹⁵N-tracing incubation experiment was conducted under controlled laboratory conditions (25°C, 35°C and 50%, 70% and 85% water filled pore space (WFPS)). Nitrification was found to be the main contributor of N₂O production, having the greatest effect at the WFPS conditions of 50% and 70% WFPS. Nitrification contributed to 87%, 80% and 53% of total N₂O production at 50%, 70% and 85%WFPS respectively at 25°C and to 86%, 74% and 33% of total N₂O production at 50%, 70% and 85%WFPS respectively at 35°C. The proportion of nitrified N as N₂O increased with increasing temperature and moisture, except at 85%WFPS. Ammonia oxidizing archaea (AOA) were the dominant ammonia oxidizers, but the ammonia oxidizing bacteria (AOB) population was significantly related to N₂O emitted from nitrification (p < 0.05). Soil moisture had a more significant (p < 0.05) influence on AOA and AOB abundance compared to soil temperature. Increasing moisture content significantly (p < 0.05) decreased AOA and AOB abundance. These findings can be used to develop better models for simulating N₂O from nitrification to inform soil management practices for improved N use efficiency.