Nitrogen Enrichment Modulates Greenhouse Gas Fluxes in Mangrove Wetlands: Microbial Mechanisms and Climate Feedback Implications

Mangroves play an essential role in sustaining and safeguarding (sub)tropical marine biodiversity and crucial ecosystem services, including serving as buffers against climate change impacts. However, the effects of nitrogen addition on greenhouse gasses (GHGs) storage and emission dynamics in mangrove wetlands remain inadequately understood. This study conducted a simulated experiment with gradient nitrogen treatments to examine how nitrogen inputs influence fluxes of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4), alongside exploring the underlying regulatory mechanisms. The results demostrated that nitrogen addition significantly altered fluxes of all three GHGs. CO2 emissions peaked at 567.19 mg/(m2·h) under the high-concentration treatment (6 mg/L NH4Cl) (P<0.05). In contrast, CH4 and N2O fluxes exhibited contrasting responses to increasing nitrogen concentration, with optimal stimulation observed at the moderate nitrogen level (4 mg/L, NH4Cl). Among measured soil parameters, total organic carbon (TOC) and ammonium (NH4+) emerged as key determinants of GHG fluxes. Elevated TOC and NH4+ levels suppressed CO2 and CH4 emissions, whileas N2O fluxes increased significantly with TOC content (P<0.05). In addition, microbial community analysis revealed that CH4 fluxes correlated strongly with methanogenic taxa (nitrosopumilus and methanolobus), while N2O emissions were more responsive to nitrospirae abundance. Additionally, CO2 and CH4 fluxes showed significant correlations with plant biomass (P<0.05), suggesting potential links to microbial respiration and vegetation growth dynamics. These findings provide valuable insights for understanding GHG emissions in mangrove wetlands and the regulatory role of nitrogen inputs, highlighting the profound implications of exogenous nitrogen loading on mangrove ecosystem functioning.