Summertime N_2O, CH_4 and CO_2 exchanges from a tundra marsh and an upland tundra in maritime Antarctica

摘要

This study provides the first concurrent measurements of nitrous oxide (N_2O), methane (CH_4) and carbon dioxide (CO_2) fluxes from a tundra marsh and an upland tundra in maritime Antarctica over the summers of 2007/2008 and 2011/2012. Tundra N_2O and CH_4 fluxes showed large spatial variations depending on local hydrological regimes. N_2O sinks generally occurred at waterlogged marsh sites (-3.0 to 27.5 μg N_2O m~(-2) h~(-1)) whereas relatively dry and mesic sites presented weak or strong N_2O sources (2.2-41.6 μg N_2O m~(-2) h~(-1)). Upland tundra sites showed negligible N_2O emissions due to low soil TN and NH~+_4-N contents. Dry/upland tundra sites showed weak to strong CH_4 uptake (-4.5 to -85.8 μg CH_4 m~(-2) h~(-1)). The waterlogged sites showed weak to strong CH_4 emissions (29.8 μg CH_4 m~(-2) h~(-1)-2.4 mg CH_4 m~(-2) h~(-1)). Both tundra marsh and upland tundra experienced a large net CO_2 uptake with the greatest mean CO_2 uptake rate (-92.1 mg CO_2 m~(-2) h~(-1)) at dry marsh sites. Mean ecosystem respiration (ER) ranged between 82.5 ± 13.2 and 174.9 ± 25.7 mg CO_2 m~(-2) h~(-1) at all the sites, and showed a strong exponential correlation (P ＜ 0.001) with 0-10 cm soil temperature. Cross photosynthesis (P_g) was more than two times higher in tundra marsh than in upland tundra due to the difference of vegetation coverage. N_2O 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 CH_4 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 N_2O emissions and CH_4 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 N_2O emission and CH_4 consumption from maritime Antarctic tundra.