极端干旱对温带草地生态系统CO_2、CH_4、N_2O通量特征的影响

Impact of Extreme Drought on the Fluxes of CO_2, CH_4 and N_2O from Temperate Steppe Ecosystems

2001年6月～9月,利用静态暗箱法,对内蒙古锡林河流域的草甸草原(包括农田和休耕地)、羊草草原、大针茅草原等典型温带草地生态系统的CO2、CH4、N2O等温室气体的通量进行了实地观测。但恰逢内蒙古地区的大旱之年,年降水量仅相当于历史正常年份的约1 6,致使干旱对温带草原生态系统的CO2、CH4、N2O通量变化影响显著。通过数据分析发现:从草原群落整个活跃生长期来看,CO2排放通量由于干旱明显减少,大约相当于1998年同期排放通量的1 5,且表现出递减趋势;温带草原对大气CH4表现为弱汇,但干旱使吸收趋于减弱,特别是草原被开垦为耕地后,干旱对其影响更明显;干旱使得大部分温带草原群落在夏季作为大气N2O源表现不明显,只有在水分状况较好的草甸草原及其被开垦的耕地和休耕地N2O排放较明显,甚至极端干旱使得温带草地生态系统对大气N2O表现出吸收特性。

Using static dark enclosed chamber technique, the fluxes of CO_2, CH_4 and N_2O from temperate steppes such as meadow (including cropland and fallow), Leymus chinensis grassland and Stipa grandis grassland in Xilin River Basin of Inner Mongolia, were measured from June to September of 2001, respectively. But there happened an extreme drought in Inner Mongolia, China in 2001; annual rainfall in 2001 was less than 1/6 of that in normal years historically (normal annual precipitation is 350 to 450 mm, most of which falls in July to September, but the total rainfall during July 20th to September 30th, 2001 was 66.7 mm in Xilinhot, Inner Mongolia). Consequently, the fluxes of CO_2, CH_4 and N_2O from grassland ecosystems were influenced distinctly by the drought that year. After analyzing the data, we found that the impact of extreme drought on the fluxes of CO_2, CH_4 and N_2O from them was very marked during the rapid growth period of grass. The significant decrease in the efflux of CO_2 (the average fluxes of CO_2 from meadow, Leymus chinensis grassland and Stipa grandis grassland were 268.7mg/(m^2h)、211.6 mg/(m^2h)、181.4 mg/(m^2h), respectively, during the measuring period), which was equal to about 1/5 of that during the corresponding period of 1998, resulted from extreme drought in 2001. And the results showed that temperate grassland ecosystem was a weak sink of atmospheric CH_4 (the average values of the influxes of CH_4 from atmosphere to grassland soil in cropland, Leymus chinensis grassland and Stipa grandis grassland ecosystems were 0.068 mg/(m^2h), 0.023 mg/(m^2h) and 0.058 mg/(m^2h), respectively) but the sink was weakened by extreme drought during the measuring period, especially in wheat field and fallow from the cultivation of meadow. That temperate grassland is the source of atmospheric N_2O did not emerge in grassland communities except meadow in 2001. Only in meadow, cropland and fallow with relatively good soil water contents, did the results show that the emissions of N_2O was evident; the drought reduced the fluxes of N_2O from meadow, cropland and fallow so much as there was a characteristic of the sink of atmospheric N_2O.