Summertime N2O, CH4 and CO2 exchanges from a tundra marsh and an upland tundra in maritime Antarctica

This study provides the first concurrent measurements of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes from a tundra marsh and an upland tundra in maritime Antarctica over the summers of 2007/2008 and 2011/2012. Tundra N2O and CH4 fluxes showed large spatial variations depending on local hydrological regimes. N2O sinks generally occurred at waterlogged marsh sites (−3.0 to 27.5 μg N2O m−2 h−1) whereas relatively dry and mesic sites presented weak or strong N2O sources (2.2-41.6 μg N2O m−2 h−1). Upland tundra sites showed negligible N2O emissions due to low soil TN and NH4+-N contents. Dry/upland tundra sites showed weak to strong CH4 uptake (−4.5 to −85.8 μg CH4 m−2 h−1). The waterlogged sites showed weak to strong CH4 emissions (29.8 μg CH4 m−2 h−1-2.4 mg CH4 m−2 h−1). Both tundra marsh and upland tundra experienced a large net CO2 uptake with the greatest mean CO2 uptake rate (−92.1 mg CO2 m−2 h−1) at dry marsh sites. Mean ecosystem respiration (ER) ranged between 82.5 ± 13.2 and 174.9 ± 25.7 mg CO2 m−2 h−1 at all the sites, and showed a strong exponential correlation (P < 0.001) with 0-10 cm soil temperature. Gross photosynthesis (Pg) was more than two times higher in tundra marsh than in upland tundra due to the difference of vegetation coverage. N2O flux showed a strong negative correlation (P < 0.01) with 0-10 cm soil temperature at the marsh sites, and significant or weak positive correlations with total daily radiation (TDR) and sunlight time (ST). No significant correlation was obtained between CH4 fluxes and environmental variables at tundra marsh and upland tundra sites. There was a significant negative correlation (P < 0.01) between NEE and 0-10 cm mean soil temperature, total daily radiation. Our results indicated that the lowering of water table significantly increased N2O emissions and CH4 consumption, but decreased C loss from the tundra marsh. In the future, the combination of climate warming and frequent precipitation will alter tundra hydrological conditions, and thus decrease N2O emission and CH4 consumption from maritime Antarctic tundra.