Subjects: Biology >> Botany >> Plant ecology, plant geography submitted time 2016-06-13
Abstract： Aims Under the global change, precipitation patterns were predicted to change with larger fluctuations in inner- and inter-annual scales and more extreme events in the semiarid regions in Northern China. Since water availability is one of the key limited factors in semiarid steppe, the changes in precipitation patterns will inevitably affect ecosystem structure and function through soil water condition. Our objectives were to study the influences of precipitation patterns on soil volumetric water content (VWC) dynamic, especially its response to precipitation pulse events. Methods Two semiarid steppe sites (Duolun and Xilinhot) in Nei Mongol were chosen and meteorological stations were installed to monitor precipitation and VWC at five depths (0–10 cm, 10 cm, 20 cm, 30 cm, 50 cm) from 2006 to 2013. The responses of surface VWC to a precipitation pulse were stimulated by an exponential equation. Important findings Significant variations of soil moisture in inner- and inter-annual scales were found at the two sites, with larger fluctuations in upper layers than the deeper ones. However, soil moisture at 50 cm depth in Xilinhot showed an obvious variation, which was due to the water infiltration from snow melting. Only mean surface soil water content of the surface layer was well correlated with annual precipitation positively but not in the deeper soil. Results showed as small as precipitation events larger than 2 mm could induce a significant increase in surface soil water content, which could be regarded as the effective precipitation events in this region. The responses of surface VWC to a precipitation pulse were simulated by an exponential equation. The maximum increment of VWC after the event (△VWC) and lasting time (Tlasting) were determined by the event size (PPT) positively, while negatively affected by the initial soil water content before the events (VWC_Pre). Additionally, vegetation (leaf area index) did not show significant impacts on the responses of VWC to precipitation pulses. The depth of infiltration after the event was also determined by PPT, and affected by VWC_Pre. In average, soil water was infiltrated 1.06 cm and 0.79 cm deeper in Duolun and Xilinhot with 1 mm more precipitation, respectively. Therefore, based on this study, the event size and VWC_Pre were most important factors affecting soil moisture’s response to precipitation event in semiarid ecosystems.
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