Diversity and Activity\nof Soil N<sub>2</sub>O‑Reducing\nBacteria Shaped by Urbanization

Nitrous oxide (N<sub>2</sub>O) is a potent greenhouse\ngas with\nvarious production pathways. N<sub>2</sub>O reductase (N<sub>2</sub>OR) is the primary N<sub>2</sub>O sink, but the distribution of its\ngene clades, typically <i>nosZ</i>I and atypically <i>nosZ</i>II, along urbanization gradients remains poorly understood.\nHere we sampled soils from forests, parks, and farmland across eight\nprovinces in eastern China, using high-throughput sequencing to distinguish\nbetween two N<sub>2</sub>O-reducing bacteria clades. A deterministic\nprocess mainly determined assemblies of the <i>nosZ</i>I\ncommunities. Homogeneous selection drove <i>nosZ</i>I deterministic\nprocesses, and both homogeneous and heterogeneous selection influenced <i>nosZ</i>II. This suggests <i>nosZ</i>II is more sensitive\nto environmental changes than <i>nosZ</i>I, with significant\nchanges in community structure over time or space. Ecosystems with\nstronger anthropogenic disturbance, such as urban areas, provide diverse\necological niches for N<sub>2</sub>O-reducing bacteria (especially <i>nosZ</i>II) to adapt to environmental fluctuations. Structural\nequation modeling (SEM) and correlation analyses revealed that pH\nsignificantly influences the community composition of both N<sub>2</sub>O-reducing bacteria clades. This study underscores urbanization’s\nimpact on N<sub>2</sub>O-reducing bacteria in urban soils, highlighting\nthe importance of <i>nosZ</i>II and survival strategies.\nIt offers novel insights into the role of atypical denitrifiers among\nN<sub>2</sub>O-reducing bacteria, underscoring their potential ecological\nimportance in mitigating N<sub>2</sub>O emissions from urban soils.