中文摘要：

水分条件是直接影响农作物产量高低的主要限制因子之一,但对青海湖流域油菜和燕麦植物水分利用方式的认识尚不清楚。论文收集油菜和燕麦整个生育期内降水、植物和土壤水氢氧稳定同位素组成,并通过直接对比法和多源混合模型定量地计算出油菜和燕麦对不同深度土壤水分利用比例。结果表明：降水中同位素组成表征出较大的波动性变化,浅层土壤水同位素组成受蒸发作用影响明显富集于深层土壤水分,且土壤水中同位素在垂直方向上呈浅层土壤水较富集于深层土壤水。油菜在生育期内根系吸水方式在浅层和深层土壤间发生明显的转换,如在蕾薹期、开花期、灌浆期及成熟期主要依赖于0~10 cm（95.1%）、0~10 cm（68%和44.8%）、30~60 cm（69.9%）及0~10 cm（38.8%）的土壤水分。而燕麦根系吸水范围却没有表征出明显的改变,在整个生育期内土壤水分利用深度在0~30 cm间变化。这将为高寒地区耕作方式调整及发展节水高效的现代农业提供理论依据。

英文摘要：

Water condition is commonly considered as an important factor affecting the yields of crops. The water use patterns of Brassica napus and Avena sativa during the growing season remain unclear in the Qinghai Lake watershed. In this paper, the stable isotope compositions in precipitation, plant xylem of Brassica napus and Avena sativa and soil water during the entire growing season were collected and the utilization ratios of soil water of the two crops were analyzed with direct comparison method and mixing Iso Source model. The results showed that the stable isotopic compositions in precipitation showed great fluctuations. The isotopic contents in shallow soil water, subject to the effect of evaporation, are more abundant than those in deep soil water. Brassica napus mainly used soil water at 0-10 cm layer at the jointing stage（95.1%）, 0-10 cm layer at the flowering stage（68% and 44.8%）, 30-60 cm layer at the filling stage（69.9%） and 0-10 cm layer at the full ripe stage（38.8%）. Avena sativa mainly utilized the soil water at 0-10 cm and 10-30 cm layers during the whole growing period. This finding provides the basis for adjusting tillage manners and developing water-saving and efficient modern agriculture in alpine regions.