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

Halomethanes (CH 3 Cl and CH 3 Br) 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 CH 3 Cl and CH 3 Br fluxes in salt marsh soil remain unclear. Thus, we investigated the mechanisms of CH 3 Cl and CH 3 Br 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 % (CH 3 Cl) and 19 % (CH 3 Br), whereas low concentration input (9.0 g N·m −2 ·a −1 ) increased gas consumption by 24 % (CH 3 Cl) and 13 % (CH 3 Br). 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 CH 3 Cl and CH 3 Br. 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.