# Urbanization-Induced Shifts in Microbial Functional Genes of Wetland Nitrogen Cycling Promote Nitrous Oxide (N2O) Emissions

## TL;DR

Urban wetlands emit more nitrous oxide due to changes in microbial communities linked to urbanization, which alters nitrogen cycling processes.

## Contribution

This study identifies microbial functional gene shifts in urban wetlands that directly enhance nitrous oxide emissions.

## Key findings

- Urbanization increased N2O fluxes 6-8 times compared to rural wetlands.
- Soil N2O emissions correlated positively with microbial alpha diversity.
- Urban wetlands enriched nitrification and denitrification genes while depleting nitrogen fixation genes.

## Abstract

Urban wetlands are assumed to contribute to nitrous oxide (N2O) emissions; however, the microbial mechanisms underlying enhanced N2O fluxes in urban wetlands and differences in microbial responses between aquatic and soil compartments have not been clearly identified. Here, we characterized the nitrogen (N) cycling microbial communities and their functional metabolic pathways in urban and rural wetlands using metagenomics and N2O flux measurements. Results showed that urbanization drove a 6~8-fold increase in N2O fluxes from urban wetlands compared to rural wetlands. Structural equation modeling (SEM) confirmed that urbanization intensity was a primary driver (standardized coefficients: 0.72 for soil and 0.92 for water). In wetland water, N2O emissions were negatively correlated with inorganic nutrient concentrations (coefficient = −0.62). Aquatic microbial communities exhibited substantial taxonomic shifts but preserved network connectivity, indicating adaptive strategies for surviving urban perturbations at the cost of reduced functional redundancy. In wetland soil, microbial communities maintained stability under urbanization, which was attributed to environmental buffering from heterogeneous microenvironments. Soil N2O emissions were positively linked to microbial alpha diversity (coefficient = 0.79). Furthermore, urban wetlands enriched genes mediating nitrification and denitrification while depleting genes associated with N fixation and organic N metabolism. This functional shift reflects microbial specialization in processing elevated reactive N (Nr) inputs from urban sources, trapping urban wetlands in an “N loss loop” that reinforces high N2O fluxes. This study elucidates the microbial mechanisms governing wetland N2O emissions under urbanization, thereby enhancing understanding of microbially mediated N cycling in the urban wetland ecosystem.