Effects of nitrogen input on halomethane fluxes via microorganism-mediated pathways in temperate salt marsh soil

Halomethanes (CH₃Cl and CH₃Br) are important atmospheric trace greenhouse gases that destroy the ozone layer. Salt marsh soils are valuable natural sources and sinks of halomethanes. The effects of nitrogen input on greenhouse gas emissions are the main driving force for greenhouse gas budgets under global climate change. However, the impacts of nitrogen input on CH₃Cl and CH₃Br fluxes in salt marsh soil remain unclear. Thus, we investigated the mechanisms of CH₃Cl and CH₃Br net emissions in Yellow River Delta salt marsh soil under different concentrations of nitrogen input. The results indicate that high concentration input (18.0 g N·m⁻²·a⁻¹) increased gas production by 7 % (CH₃Cl) and 19 % (CH₃Br), whereas low concentration input (9.0 g N·m⁻²·a⁻¹) increased gas consumption by 24 % (CH₃Cl) and 13 % (CH₃Br). Nitrogen input affected halomethanes net emission fluxes via physicochemical properties and microorganism-mediated pathways in temperate salt marsh soil. First, soil organic carbon (SOC) and dissolved organic matter (DOM) are the main factors that affected the net emissions of CH₃Cl and CH₃Br. High concentration input directly increases the contents of SOC and DOM, stimulating the production of halomethanes. Second, changes in soil nutrients after nitrogen input indirectly inhibited the abundance of Actinobacteria, inhibiting the consumption of halomethanes. The abiotic production and biodegradation processes in the soil jointly determined the net emission fluxes of halomethanes. High nitrogen pollution would further enhance the net emission fluxes of halomethanes under the context of continuous global nitrogen input.