中文摘要：

在全球气候变化背景下,未来我国北方半干旱地区的降水格局将呈现出季节与年际间降水波动增强和极端降水事件增加的趋势。水分是半干旱草原的主要限制因子,降水格局变化导致的土壤水分状况的改变必然对生态系统的结构和功能产生显著的影响。该研究选取内蒙古多伦和锡林浩特两个典型半干旱草原群落,通过分析2006–2013年的降水和多层次土壤（0–10 cm,10 cm,20 cm,30 cm和50 cm）含水量连续观测数据,研究降水格局变化对土壤水分状况及其垂直分布的影响,特别是土壤水分对降水事件的脉冲响应过程。结果表明：两个站点的土壤含水量均呈现显著的季节及年际间波动,其中土壤表层0–10 cm水分波动更剧烈。锡林浩特50 cm处土壤含水量波动较大,主要由于春季融雪的影响。年际间多伦和锡林浩特生长季土壤表层0–10 cm土壤含水量与降水量存在显著的正相关关系,下层（10–50 cm）土壤含水量与降水量相关性不显著。研究发现小至2 mm的降水事件就能够引起两个站点表层0–10 cm土壤含水量的升高,即该地区有效降水为日降水量〉2 mm。表层0–10cm土壤含水量对独立降水事件的脉冲响应可通过指数方程很好地拟合。降水事件的大小决定了降水后表层0–10 cm土壤含水量的最大增量和持续时间,同时这个脉冲响应过程还受到降水前土壤含水量的影响,但该过程中并未发现植被因子（叶面积指数）的显著影响。降水后水分下渗深度及该深度的土壤含水量增量主要由降水事件的大小主导,同时受到降水前土壤含水量的影响。在多伦和锡林浩特,平均每增加1 mm降水,下渗深度分别增加1.06和0.79 cm。由此作者认为,在内蒙古半干旱草原,降水事件大小和降水前土壤干湿状况是影响土壤水分对降水响应的主要因素,而植被因子的影响较小。

英文摘要：

Aims Under global climate change, precipitation patterns were predicted to change with larger seasonal and annual variations and more extreme events in the semiarid regions of northern China. Water availability is one of the key limited factors in semiarid grasslands. Changes in precipitation patterns will inevitably affect ecosystem structure and function through soil water condition. Our objective was to investigate the response of soil water content to changes of precipitation pattern, especially its pulse response to precipitation events. Methods Two semiarid steppe sites（Duolun and Xilinhot） in Nei Mongol were chosen and meteorological stations were installed to monitor precipitation and soil volumetric water content（VWC） at five soil depths（0–10 cm, 10 cm, 20 cm, 30 cm, 50 cm） from 2006 to 2013. The pulse response of VWC at 0–10 cm to an individual precipitation event was simulated by an exponential equation. Important findings Significant seasonal and inter-annual variations of VWC were observed at the Duolun and Xilinhot sites. VWC at 50 cm soil layer in Xilinhot showed an obvious increase during the early spring due to the influences of snow melting. Mean surface（0–10 cm soil layer） VWC was significantly correlated with annual precipitation across eight years, but VWC in the deeper soil layers（10–50 cm） were not impacted by precipitation. We also found that the precipitation event larger than 2 mm could induce a significant increase in surface（0–10 cm soil layer） VWC, and could be regarded as an effective precipitation in this region. The maximum increment ofsurface VWC after the events and lasting time（Tlasting） were determined by the event size, while showed negatively linear correlations with the initial soil water content before the events. Vegetation development（leaf area index） did not show significant impacts on the responses of surface soil moisture to precipitation pulses. The infiltration depth of rain water was also determined by rain size and pre-even