Short-term effect of increasing nitrogen deposition on CO 2, CH 4 and N 2O fluxes in an alpine meadow on the Qinghai-Tibetan Plateau, China

Abstract

An increasing nitrogen deposition experiment (2 g N m −2 year −1) was initiated in an alpine meadow on the Qinghai-Tibetan Plateau in May 2007. The greenhouse gases (GHGs), including CO 2, CH 4 and N 2O, was observed in the growing season (from May to September) of 2008 using static chamber and gas chromatography techniques. The CO 2 emission and CH 4 uptake rate showed a seasonal fluctuation, reaching the maximum in the middle of July. We found soil temperature and water-filled pore space (WFPS) were the dominant factors that controlled seasonal variation of CO 2 and CH 4 respectively and lacks of correlation between N 2O fluxes and environmental variables. The temperature sensitivity ( Q 10) of CO 2 emission and CH 4 uptake were relatively higher (3.79 for CO 2, 3.29 for CH 4) than that of warmer region ecosystems, indicating the increase of temperature in the future will exert great impacts on CO 2 emission and CH 4 uptake in the alpine meadow. In the entire growing season, nitrogen deposition tended to increase N 2O emission, to reduce CH 4 uptake and to decrease CO 2 emission, and the differences caused by nitrogen deposition were all not significant ( p < 0.05). However, we still found significant difference ( p < 0.05) between the control and nitrogen deposition treatment at some observation dates for CH 4 rather than for CO 2 and N 2O, implying CH 4 is most susceptible in response to increased nitrogen availability among the three greenhouse gases. In addition, we found short-term nitrogen deposition treatment had very limited impacts on net global warming potential (GWP) of the three GHGs together in term of CO 2-equivalents. Overall, the research suggests that longer study periods are needed to verify the cumulative effects of increasing nitrogen deposition on GHG fluxes in the alpine meadow.