中文摘要：

采用盆栽试验,分析了不同水分梯度下（田间持水量的30％、40％、50％、60％和85％）头状沙拐枣幼苗的干物质累积分配特征及生理生化特性,以探明头状沙拐枣幼苗能够良好生长的土壤水分条件.结果表明：（1）随灌溉量增加,沙拐枣幼苗同化枝的干物质累积量显著增加,但在最高灌溉量下同化枝出现严重病害.（2）在生长旺季,增加灌溉量后,同化枝的干物质分配比例也均显著增加,平均可占整株的39.5％;季末,分配比例受灌溉量的影响明显减弱,平均占整株的12.3％.（3）在整个生长季同化枝的全氮和硝态氮含量均处于较高水平,随灌溉量增加全氮含量有降低趋势,硝态氮含量则波动变化.（4）灌溉量对植株同化枝生理特性的影响主要表现在生长旺季.在最低灌溉量下,同化枝丙二醛含量明显较高,但植物可通过大量累积脯氨酸和可溶性糖来降低体内水势,以提高植物抗旱性;在最高和最低灌溉量下,同化枝硝酸还原酶活性和叶绿素含量均显著下降.研究认为,沙拐枣幼苗虽具有较强的抗旱性,但灌溉量过低或过高对同化枝的生长、氮素还原和叶绿素累积均有明显的抑制,因此中等灌溉量（田间持水量的50％～60％）对头状沙拐枣幼苗生长更有利.

英文摘要：

A pot experiment was carried out to study the growth,N nutrition,and physiological characteris- tics of Calligonurn caput-medusae seedlings under different irrigation treatments （30%, 40%, 50%, 60%, and 85% field water capacity （FWC））,and further to find out the suitable water condition to improve the plant growth. The results showed that ： （1） Dry weight of the assimilating branches significantly increased with increasing amounts of irrigation. However, C. caput-medusae seedlings were infected with powdery mildew at the high irrigation level （85 %FWC）. （2）During the early growth stage, the assimilating branches, as growth center, accounted for 39.5% of the average whole-plant dry matter accumulation. Irrigation significantly promoted dry matter allocation to assimilating branches. During the late growth stage, the plants allocated less dry matter into assimilating branches, accounting for an average of 12.3% of wholeplant dry matter accumulation. In addition, the allocation proportion was not correlated with irrigation amounts. （3）The assimilating branches had high N and nitrate-N concentrations throughout the whole growth season. The N concentration of assimilating branches decreased, but the nitrate-N concentration had a fluctuation change with increasing amounts of irrigation. （4）The effects of irrigation on physiological characteristics of C. caput-medusae seedlings mainly occurred in the early growth stage. The nitrate reductase activity and chlorophyll content of assimilating branches were significantly limited under the low and high irrigation treatments （30% and 85 % FWC）. The plants had great MDA, soluble sugar and proline contents,but lower water potential under the lowest irrigation treatment. The MDA and proline contents decreased,but water potential and soluble sugar content increased with increasing amounts of irrigation. This suggested that C. caput-medusae seedlings had strong osmotic adjustment capacity to adapt to water stress. However, medium irrigation levels