北京山区侧柏-荆条系统水分来源对降雨事件的响应

Response of water sources in Platycladus orientalis and Vitex negundo var. heterophylla system to precipitation events in mountain area of Beijing,China

分析了北京鹫峰山区侧柏、荆条枝条水及其潜在水分来源的氢氧同位素特征,运用Iso Source模型解析侧柏、荆条系统水分利用来源的季节变化及其对降雨事件的响应.结果表明:旱季初期(4月)研究区0~20 cm土层富集土壤水^(18)O值,20 cm以下该值则随着土层深度增加逐渐减小,侧柏主要利用前2~3 d降雨补充的0~30 cm层土壤水;旱季末期(6月)侧柏和荆条分别利用当天雨水补充的0~10和10~30 cm层土壤水;雨季(7月)侧柏利用前期降水补给的0~40 cm层土壤水(59.3%)和近期降水(12.5%),荆条则利用近期降雨供给的0~30 cm层土壤水;侧柏的土壤水分来源逐月加深,至生长季末(11月)其主要利用60~80 cm层土壤水(前2~3 d降雨补给),而荆条枝条水δ^(18)O值远离各水分来源δ^(18)O值.两物种对水分的竞争压力小,适应本区域气候特征,尤其在应对特大暴雨等极端天气时,植物系统垂直分布的水分来源能够有效分流洪峰,减小暴雨瞬时破坏力.

This study aimed to qualify the potential water sources and their responses to seasonal precipitations for the system of Platycladus orientalis and Vitex negundo var. heterophyUa by Iso- Source model based on stable hydrogen and oxygen isotopic analysis in Jiufeng Mountain area of Beijing. The results showed that the 180 of water from 0-20 cm soil layer was enriched, whereas that was depleted as the soil layer deepened. P. orientalis used water mainly from 0-30 cm soil la- yer, being composed of rainwater 2-3 days before at the beginning of dry season. The water ab- sorbed by P. orientalis and V. negundo sourced from 0-10 cm and 10-30 cm soil layer, which was fed on recent rainwater at the end of dry season. In wet season P. orientalis mainly accessed the soil water （from 0-40 cm layer, 59.3%） and recent rainwater （12.5%） , while V. negundo drank the water from 0-30 cm soil layer derived from recent heavy rain. P. orientalis actively uptook the dee- per soil water with time, until the end of growing season （November） , its available water was from 60-80 cm soil layer and sourced from the rainwater happened 2-3 days before. Meanwhile, V. ne- gundo completed its growing cycle and was on the brink of death. This system faced less competition for water use, stating its vertical water availability for climate adaptation in this region, which could reduce water and soil loss and minimize the instantaneous damage under heavy rainstorm attack.