Climatic temperature controls the geographical patterns of coastal marshes greenhouse gases emissions over China

Coastal marshes contribute greatly to atmospheric greenhouse gases (GHGs) and have thus attracted considerable attention at regional and global scales. However, the relative importance of climates and soil variables to the geographical variation of GHG emissions at a large geographical scale remains poorly understood. We thus investigated the spatial patterns of GHG (CO₂, CH₄ and N₂O) emissions from coastal marshes along a latitudinal gradient in China and identified the climatic and soil variables controlling the emissions. Emissions of CO₂, CH₄ and N₂O were estimated at rates of 12.8–310 mg CO₂ m^–2 h⁻¹, 23.6–986 µg CH₄ m^–2 h⁻¹ and 1.58–110 µg N₂O m^–2 h⁻¹, respectively. The emissions of CH₄, N₂O and CO₂ increased from high to low latitudes and were strongly correlated with climatic temperature. These emissions also varied significantly between temperate and subtropical climates and between winter and summer. Soil Eh, total organic carbon (TOC), dissolved organic carbon (DOC), total nitrogen, microbial biomass carbon (MBC) and nitrogen (MBN), bacterial abundance were the key regulators of CH₄ emissions. Soil Eh, TOC, DOC, MBC and MBN were the crucial variables controlling N₂O emissions. CO₂ emissions across the coastal marshes were controlled mainly by soil pH, TOC, DOC, MBC, MBN and bacterial abundance. Although GHG emissions were strongly correlated with climatic temperature, 28–67% of the variations in GHG emissions were attributed to soil variables. The relative amplitudes (%) of the increases in GHG emissions, estimated on the basis of projected annual increases of 2 or 4 °C by 2100, were larger in temperate than subtropical coastal marshes, indicating that the coastal marshes with lower temperature were more sensitive to global warming. The annual emissions of CO₂, CH₄ and N₂O estimated from the Chinese coastal marshes accounted for 6.6, 0.62 and 0.70‰ of the annual emissions from global terrestrial ecosystems, respectively. These results suggest that coastal marshes will be important to future global warming and will play a critical role in global GHG emissions.