中文摘要：

地处塔克拉玛干沙漠南缘的荒漠-绿洲过渡带常年平均降水量仅为35 mm左右，而在2010年，该地区却发生了偶发性强降水。对于多年生植物来说，如何去适应这种短期强降水，我们都不得而知。在此背景下，我们对该地区头状沙拐枣幼苗的形态特征和生长特点等进行了定位试验研究。结果表明：在头状沙拐枣幼苗期，水分条件与其株高、冠幅、基径、根深等形态特征指标以及种群密度呈正相关；增加根冠比是沙拐枣幼苗适应干旱的有效策略；在7、8月，根冠比随水分条件的减少而增加，它们在生长初期把更多生物量分配到地上用以竞争光照资源，生长后期把更多生物量分配到根系用以探索地下空间资源；沙拐枣幼苗能随水分改变而自我调节生长比例来适应环境，不同水分条件下其株高-基径生长均属于典型的异速生长关系。这些结果在一定程度上反映了不同水分条件下头状沙拐枣幼苗生长规律，可为塔克拉玛干沙漠南缘地区植被恢复提供理论依据。

英文摘要：

In the desert-oasis transitional zone in southern fringe of Taklimakan Desert, Xinjiang of Northwest China, the mean annual precipitation is only about 35 mm, but occasional strong precipitation sometimes happens, like the event in 2010. How the perennial species adapt to the short-term heavy precipitation is less known. In this paper, a site-specific field investigation was conducted to understand the morphological and growth characteristics of Calligonum caputmedusae Schrenk under different soil water conditions. At seedling period, the morphological characteristics （including plant height, crown width, basal diameter, and root depth） and population density of C. caputmedusae were positively correlated with soil water content, and increasing root/shoot ratio was an effective strategy of C. caputmedusae to adapt to soil water shortage. Especially in July and August, the root/shoot ratio increased with decreasing soil water content. The plants allocated more biomass into aboveground part in their early growth period to compete for light resource, and allocated more biomass into root in the late growth period to explore underground space resources. The seedlings could selfregulate their growth proportion to adapt the environment when soil water content changed. An allometric relationship between plant height and basal diameter was always observed under different soil water condition. To some extent, these results reflected the growth pattern of the C. caputmedusae seedlings under different soil water conditions, and provided theoretical support for the vegetation restoration in the south fringe of the Taklamakan Desert.