Ammonia-oxidizing bacteria are the primary N2O producers in long-time tillage and fertilization of dryland calcareous soil

Human intervention in agriculture, such as tillage and fertilization, could result in major changes of N2O emissions that understanding the N2O emission mechanism is of great significance in reducing the N2O emissions of the agricultural system. In this work, we focused on the conventional tillage practice and straw return practice used in the spring maize production system of this region and compared them by the addition of 3,4-dimethylpyrazole phosphate (DMPP) to explore the N2O emission mechanism of the farmland. Compared with conventional farming, straw return significantly increased the N2O emissions from the soil. Soil pH had important effects on soil N2O emissions through its influence on the ammonia oxidizer community. In addition, DMPP was used to distinguish N2O emissions driven by ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), and the results showed that AOB were the dominant factor regulating N2O emissions after receiving nitrogen from an external source in dryland farming calcareous soil. Through the analyses of soil AOB community composition and the aggregated boosted tree (ABT) model for N2O emissions, Nitrosospira Cluster 3a.2 was found to be the main driving force of soil N2O emissions in AOB communities. These findings will help better understand the physiochemical and biological mechanisms underlying the N2O emissions of agricultural soils and provide insight for reducing the negative impact of agricultural production systems on the ecological environment.