Diversity and Activity of Soil NO-Reducing Bacteria Shaped by Urbanization.

Nitrous oxide (NO) is a potent greenhouse gas with various production pathways. NO reductase (NOR) is the primary NO sink, but the distribution of its gene clades, typically I and atypically 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 NO-reducing bacteria clades. A deterministic process mainly determined assemblies of the I communities. Homogeneous selection drove I deterministic processes, and both homogeneous and heterogeneous selection influenced II. This suggests II is more sensitive to environmental changes than 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 NO-reducing bacteria (especially II) to adapt to environmental fluctuations. Structural equation modeling (SEM) and correlation analyses revealed that pH significantly influences the community composition of both NO-reducing bacteria clades. This study underscores urbanization's impact on NO-reducing bacteria in urban soils, highlighting the importance of II and survival strategies. It offers novel insights into the role of atypical denitrifiers among NO-reducing bacteria, underscoring their potential ecological importance in mitigating NO emissions from urban soils.