Abstract：【Objective】Greenhouse vegetable systems, characterized by greenhouse covering, intensive fertilization, and frequent irrigation, create a semi-closed, warm, and humid microenvironment that more readily intensifies nitrification-driven nitrogen losses and greenhouse gas emissions compared with open-field vegetable systems. Greenhouse and open-field vegetable systems differ markedly in their environmental conditions, which may lead to variations in the intensity of nitrification and the level of nitrous oxide (N2O) production. However, the seasonal dynamics of nitrification activity and N2O production, as well as the underlying community response mechanisms under different management practices, remain poorly understood. 【Method】Soil samples were collected bimonthly (January to November) from representative greenhouse and open-field vegetable systems in Changshu, Jiangsu Province, China. Meanwhile, in situ N2O was collected from the vegetable field using the static chamber method. A microcosm experiment with combined inhibitors was employed to quantitatively assess the annual dynamics of nitrification activity and N2O production driven by complete ammonia-oxidizing bacteria (Comammox) and conventional ammonia-oxidizing microorganisms (Ammonia-oxidizing bacteria, AOB and Ammonia-oxidizing archaea, AOA). The absolute abundances of these microbial groups were determined using quantitative real-time PCR (qPCR) targeting the amoA gene. Additionally, high-throughput sequencing of the amoA gene was conducted to characterize the seasonal shifts in community structure and their responses to different management regimes. 【Result】Results showed that in situ N2O flux in greenhouse vegetable soils was significantly higher than that in open-field vegetable soils, with a pronounced “hot-moment effect” in March and May, contributing 71.23±25.50% of the annual total flux. Soil nitrification activity exhibited a pronounced “hot-moment” effect in July and September, accounting for 52.41±1.59% of the annual total, which coincided with the highest N2O production potential (61.35±9.24% of the annual release). Functionally, the nitrification process and N2O production were predominantly mediated by ammonia-oxidizing bacteria (AOB) in greenhouse vegetable soils, whereas ammonia-oxidizing archaea (AOA) dominated in open-field vegetable soils. Greenhouse vegetable system promoted the accumulation of Comammox abundance but suppressed its nitrification function, whereas both the abundance and activity of AOB were significantly enhanced. Correlation analysis revealed that soil temperature, dissolved organic carbon (DOC) and soil pH were the primary drivers of nitrification, while nitrate and DOC were the main factors shaping microbial community composition. 【Conclusion】This study elucidated the influence of differentiated management practices on the nitrification processes of soil nitrifying microorganisms, and demonstrated that the shift from open-field to greenhouse vegetable systems may increase AOB-driven N2O production. These findings provide a scientific foundation for optimizing nitrogen management and developing N2O mitigation strategies in vegetable cultivation systems.