中文摘要：

黄土丘陵区属于季节性干旱的区域,研究退耕生态系统植被根系分布及其水分利用特征对植被恢复具有重要意义。该研究利用稳定同位素技术,采集黄土区5种典型退耕植被群落的根系、土壤样品,分析根系形态结构和稳定同位素特征,探讨根系在不同季节的吸水策略。结果显示：旱季茵陈蒿、铁杆蒿、白羊草、达乌里胡枝子群落和油松的根长密度（16.3、21.7、17.3、17.3、6.0 mm/cm3）分别是雨季（1.7、2.1、3.2、5.9、4.2 mm/cm3）的9.4、10.2、5.3、2.9、1.4倍,茵陈蒿、铁杆蒿、白羊草根系对土壤水分季节变化的响应较为敏感。茵陈蒿群落仅可利用0~10 cm土壤水,旱季铁杆蒿、白羊草群落主要利用30~40 cm土壤深度的水分,雨季吸水深度上移至0~20 cm。旱季达乌里胡枝子和油松主要利用60 cm以下的土壤水分,雨季则吸收20~40 cm土壤水分。表明退耕植被群落根系在不同季节的吸水策略不同,旱季吸收较深的土壤水而雨季则吸收近地表的土壤水,吸水深度范围的季节变化与土壤水和根系分布变化相一致。该研究为黄土丘陵区退耕植被对流域生态水文过程影响的研究提供科学依据。

英文摘要：

Soil water is a key limiting factor for plant growth,species richness,primary productivity and grassland stability in arid and semi-arid area all over the world.Root system is the linkage between vegetation and soil for material circulation and energy transformation.Since the Chinese government implemented ＂Grain for Green＂ project in 1999,lots of annual croplands was converted to perennial native vegetation,which had significantly altered the eco-hydrological cycle in the Loess Hilly Region.The evaluations of root morphology and water-using characteristics of different vegetations abandoned from croplands are benefit to understand the effect of different vegetation communities on hydrologic cycle and provide theory guidance for vegetation restoration in semi-arid area.In this study,soil and root samples of 5 differents vegetation communities（Artemisia capillaris,A.sacrorum,Bothriochloa ischaemun,Lespedeza davurica and Pinus tabulaeformis） were collected in dry and wet seasons of 2015 in Wangmaogou watershed of Wuding River.The root morphological structures and signatures of stable isotopes were determined by using stable isotope technology.Each vegetation communities was arranged in the 2-3 plots as repeat,arranged 2 plots in Artemisia capillaris,A.sacrorum,Bothriochloa ischaemun and Lespedeza davurica,respectively,arranged 3 plots in Pinus tabulaeformis.Then 5 quadrats were established in each kind of plots.Ensured the same distances between collection points and the shrubs or trees when sampling in Lespedeza davurica or Pinus tabulaeformis,and to avoid the error caused by the different horizontal distances from the stems of the plant（For examples,root biomass,soil water contents,etc.）.The results showed that the RLDs（Root length densities） of A.capillaris,A.sacrorum,B.ischaemun,L.davurica and P.tabulaeformis in dry season（16.3,21.7,17.3,17.3,6.0 mm/cm3） were 9.4,10.2,5.3,2.9 and 1.4 times compared that in wet season（1.7,2.1,3.2,5.9,4.2 mm/cm3）,respectively.The root systems of A.capillar