Wetlands contribute considerably to the global greenhouse gas (GHG) balance. In these ecosystems, groundwater level (GWL) and temperature, two factors likely to be altered by climate change, exert important control over CO2, CH4 and N2O fluxes. However, little is known about the temperature sensitivity (Q10) of the combined GHG emissions from hydromorphic soils and how this Q10 varies with GWL. We performed a greenhouse experiment in which three different (plant-free) hydromorphic soils from a temperate spruce forest were exposed to two GWLs (an intermediate GWL of −20 cm and a high GWL of −5 cm). Net CO2, CH4 and N2O fluxes were measured continuously. Here, we discuss how these fluxes responded to synoptic temperature fluctuations. Across all soils and GWLs, CO2 emissions responded similarly to temperature and Q10 was close to 2. The Q10 of the CH4 and N2O fluxes also was similar across soil types. GWL, on the other hand, significantly affected the Q10 of both CH4 and N2O emissions. The Q10 of the net CH4 fluxes increased from about 1 at GWL = −20 cm to 3 at GWL = −5 cm. For the N2O emissions, Q10 varied around 2 for GWL = −20 cm and around 4 for GWL = −5 cm. This substantial GWL-effect on the Q10 of CH4 and N2O emissions was, however, hardly reflected in the Q10 of the total GHG emissions (which varied around 2), because the contribution of these gases was relatively small compared to that of CO2.
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