Diversity and Activity of Soil N 2 O-Reducing Bacteria Shaped by Urbanization.

Nitrous oxide (N 2 O) is a potent greenhouse gas with various production pathways. N 2 O reductase (N 2 OR) is the primary N 2 O sink, but the distribution of its gene clades, typically nosZ I and atypically nosZ II, along urbanization gradients remains poorly understood. Here we sampled soils from forests, parks, and farmland across eight provinces in eastern China, using high-throughput sequencing to distinguish between two N 2 O-reducing bacteria clades. A deterministic process mainly determined assemblies of the nosZ I communities. Homogeneous selection drove nosZ I deterministic processes, and both homogeneous and heterogeneous selection influenced nosZ II. This suggests nosZ II is more sensitive to environmental changes than nosZ I, with significant changes in community structure over time or space. Ecosystems with stronger anthropogenic disturbance, such as urban areas, provide diverse ecological niches for N 2 O-reducing bacteria (especially nosZ II) to adapt to environmental fluctuations. Structural equation modeling (SEM) and correlation analyses revealed that pH significantly influences the community composition of both N 2 O-reducing bacteria clades. This study underscores urbanization's impact on N 2 O-reducing bacteria in urban soils, highlighting the importance of nosZ II and survival strategies. It offers novel insights into the role of atypical denitrifiers among N 2 O-reducing bacteria, underscoring their potential ecological importance in mitigating N 2 O emissions from urban soils.