摘要:沙地柏、黑沙蒿和沙柳是毛乌素沙地的3种优势灌木群落。利用稳定同位素技术研究了3种灌木及伴生植物杨柴主要利用的水分来源，结合叶片稳定碳同位素值与土壤水分监测，从而确定灌木群落如何利用水分。结果表明：7月和9月3种群落内浅层土壤水的稳定氧同位素值接近雨水。沙地柏5月主要利用25 cm浅层土壤水，而7月和9月主要利用10-25 cm浅层和100-200 cm深层土壤水。黑沙蒿和伴生的杨柴5月主要利用10 cm浅层土壤水，7月同时利用10 cm浅层土壤水和150 cm深层土壤水，9月则利用10-150 cm土壤水。沙柳5月主要利用10-25 cm浅层土壤水，伴生的杨柴主要利用50-200 cm土壤水；7月它们同时利用10-25 cm浅层土壤水和100-200 cm深层土壤水；9月都主要利用25-200 cm土壤水。4种植物的叶片稳定碳同位素值存在季节动态和种间差异。常绿灌木沙地柏的叶片碳同位素值比较稳定，而且高于其他3种落叶灌木和半灌木。5月浅层土壤含水量较低时3种落叶植物的叶片碳同位素值较高。因此，降雨补充的浅层土壤水是3种灌木群落利用的主要水分来源。3种灌木及其伴生植物根据不同深度土壤水的可利用性，在不同季节利用不同深度的土壤水。杨柴与黑沙蒿或沙柳均存在水分竞争。沙地柏的叶片稳定碳同位素值较高，干旱时具有竞争优势。干旱时落叶灌木和半灌木能够提高叶片稳定碳同位素值来适应环境。



Abstract:In Mu Us Sandy Land, Sabina vulgaris, Artemisia ordosica, and Salix psammophila are the three dominant shrub communities. The water source of the three dominant shrubs and the associated shrub Hedysarum laeve were investigated by stable isotope technology, and leaf stable carbon isotope composition and soil water dynamics were monitored to clarify how these shrub communities utilize water. The results showed that the δ¹⁸O of shallow soil water in shrub communities was similar to that of rainwater in July and September. S. vulgaris mainly used shallow soil water (25 cm) in May, and mainly used both shallow (10-25 cm) and deep (100-200 cm) soil water in July and September. A. ordosica and its associated plant H. laeve mainly used surface soil water (10 cm) in May, but used surface soil water and deep soil water in July (10 cm and 150 cm) and water from the total soil profile (10-150 cm) in September. S. psammophila mainly used shallow soil water (10-25 cm) in May, where as its associated plant H. laeve mainly used deep soil water (50-200 cm); in contrast, both used shallow and deep soil water in July (10-25 cm and 100-200 cm) and in September (25-200 cm). There were seasonal and inter-specific variances among leaf δ¹³C value of the four plants. The evergreen shrub S. vulgaris had a constant leaf δ¹³C value, which was higher than for the three deciduous shrubs. The leaf δ¹³C value of three deciduous plants was higher in May when the soil water content was lower at a shallow depth. Therefore, shallow soil water that was recharged by rainwater was the main water source for three shrub communities. Based on the availability of soil water, the three shrub communities utilized different depths of soil water in different seasons. There was water competition between H. laeve and A. ordosica or S. psammophila. The evergreen shrub S. vulgaris had a higher leaf stable carbon isotope composition, which may confer a competitive advantage. Deciduous shrubs or semi-shrubs may adapt to the environment by enhancing leaf δ¹³C value during drought.





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