Responses of soil moisture to precipitation pattern change in semiarid grasslands in Nei Mongol, China

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 of ©植物生态学报 Chinese Journal of Plant Ecology 陈敏玲等: 内蒙古半干旱草原土壤水分对降水格局变化的响应 659 doi: 10.17521/cjpe.2015.0155 surface 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-event soil moisture. In average, soil water can infiltrate 1.06 cm and 0.79 cm deeper in Duolun and Xilinhot with 1 mm more precipitation, respectively. Therefore, our results suggest that the event size and pre-event soil moisture were the most important factors affecting response patterns of soil moisture to rain events in semiarid ecosystems.