中文摘要：

【目的】研究西鄂尔多斯荒漠珍稀濒危植物半日花及霸王对不同强度降水的利用模式,以期阐明植物的生长规律和分布趋势及其对降水变化的适应机制,为荒漠珍稀濒危植物保护提供参考。【方法】利用氢稳定同位素技术,分析比较3次不同强度降水后9天内,半日花、霸王植物（茎）水δD与其潜在水源（降水、土壤水、地下水）δD,定量阐明半日花、霸王对不同强度降水的利用率。【结果】1）8.6 mm降水后9天内,0～20 cm表层土壤含水量明显上升、土壤水δD降低,12.1 mm降水后9天内,0～40 cm土壤含水量和土壤水δD变化明显,79.6 mm降水后9天内,各层土壤含水量显著上升、土壤水δD降低;2）降水后9天内,半日花和霸王对大雨（〉20 mm）的利用率最高,分别为76.4%～98.5%和55.6%～74.3%;半日花对小雨（〈10 mm）的最高利用率为67.0%,对中雨的最高利用率为71.8%,表明半日花可充分吸收利用有限的水分,并最大限度地利用该地区大气降水,以更好地生存和生长;3）在3种不同降水强度下,半日花对降水的利用率皆显著高于其伴生植物霸王;4）在中等降水强度（10 mm〈降水量≤20 mm）条件下,霸王和半日花存在明显的竞争水分现象,在小降水强度（〈10 mm）条件下,霸王和半日花利用不同深度土壤水,无水分竞争现象;5）半日花的根系主要分布在0～40 cm土层中,细根在0～20和20～40 cm土层中分别占该层根系生物量的58%和37%;霸王根系主要分布在20～60 cm土层,其中细根（≤2 mm）在20～60 cm土层中分布最多（68.2%）。【结论】小雨（〈10 mm）对表层土壤水（0～20 cm）δD有影响,中雨（10 mm〈降水量≤20 mm）对0～40 cm土壤水δD有影响,大雨（〉20 mm）对各层土壤水δD均有明显影响;半日花对不同强度降水均能充分有效地利用,霸王对大雨有明显的响应,这2种植物的水分利用策略与其细根分布相一致。

英文摘要：

【Objective】Helianthemum songaricum is a rare and endangered relict perennial xeric shrubs in western Ordos. Water plays an important role in the growth and function of desert plants,and precipitation is the main water source in arid and semiarid regions. Therefore researches on the water use patterns of desert plants under different intensities of rain events are helpful to understand the growth regulation and distribution tendency of plants and their response mechanism to rainfall.【Method】To quantify the utilization of rains with different pulse intensities by H. songaricum and Sarcozygium xanthoxylum,we established and analyzed relationships between plant xylem water of H. songaricum and S.xanthoxylum and potential water（ precipitation,soil water and ground water） within 9 days following each natural rain eventusing hydrogen stable isotopes.【Result】1） We found that the soil moisture increased and soil water δ Ddecreased in the surface soil of 0- 20 cm after 8. 6 mm within 9 days,and the soil moisture and soil water δ Dchanged obviously in the soil of 0- 40 cm after 12. 1 mm within 9 days,whereas the soil moisture and soil water δ Dchanged significantly in all soil depth after 79. 6 mm with in 9 days. 2） For the three rain events observed,the utilization rate of rain water by H.songaricum and S. xanthoxylum within 9 days was the highest under the large rain event（ 〉20mm） at 76. 4%- 98. 5%and 55. 6%- 74. 3% respectively. The highest utilization rate of rain water by H. songaricum within 9 days was 67. 0%under the small rain event（ 〈10 mm） and 71. 8% under the intermediate event. It is indicated that H. songaricum could use the limited rain water effectively,which could greatly improve its chance for survival. 3） The utilization rate of rain water by H. songaricum was significantly higher than that by S. xanthoxylum in despite of the intensities of rain events. 4）In the intermediate rain event,the competition between H. songaricum and S. xanthoxylum for the soil water was obv