中文摘要：

通过盆栽控水实验，模拟科尔沁沙地由东至西50年的年均降水量及最大、最小年降水量下的土壤水势，分析了不同水分处理（土壤水势分别为-16．18、-5．09和-4．50bars，即A、B和C处理）对樟子松2年生幼苗膜脂过氧化产物[丙二醛（MDA）、脂膜相对透性（RC）和超氧阴离子自由基（O2^-）产生速率]、渗透调节物质[可溶性糖（SS）、可溶性蛋白（SP）和脯氨酸（Pro）]和膜保护酶（SOD酶和POD酶）的影响。不同水分处理对樟子松幼苗针叶内的保护酶、渗透调节物质及膜脂过氧化的作用影响显著。随着土壤水势的降低，幼苗的SOD酶呈现微下降再升高的趋势；POD酶活性呈逐渐升高的趋势；幼苗的渗透调节物质（SS、SP和Pro）的含量均呈现上升趋势；3种水分处理的可溶性糖和可溶性蛋白含量上升的幅度最大，A处理分别是C处理的1．8倍和2．4倍，脯氨酸的含量持续积累；随干旱胁迫加重，MDA、RC和O2^-产生速率均有明显上升趋势，以O2^-产生速率上升幅度最大。这表明，樟子松幼苗通过体内的生理生化机制，尤其是增加渗透调节物质的含量，实现对干旱胁迫较强的忍耐性和较好的适应性。A处理针叶内的自由基大量积累和膜脂过氧化程度加重，对植物造成不可逆的损伤。

英文摘要：

Mongolian pine （Pinus sylvestris var. mongolica） has been widely planted on sandy soil in northern region of China, but a decline in forest growth and even death has occurred in the earliest Mongolian pine plantations on Keerqin sandy soil located at Zhanggutai of Liaoning Province. Aiming to study the decline problem of Mongolian pine, a water gradient experiment was conducted to assess the effects of soil water stress on the membrane lipid peroxidation, osmotic substances, and protective enzyme system of two-year old P. sylvestris var. mongolica seedling＇ s needles. The water gradient experiment was designed with reference to the annual mean precipiration of main sites on Keerqin over 50 years. The results showed that with the aggravation of drought stress, the SOD activity of the seedling＇ s needles increased after an initial slight decrease, while POD activity had gradually increased. The osmotic substances including soluble sugar （SS）, soluble protein （SP） and proline （Pro） presented distinct ascending trend with drought stress, and the ascending range was the largest for SS and SP, e. g. , the contents of SS and SP at -16. 18 bars were 1.8 and 2.4 times than those at -4.50 bars, respectively. The MDA content, plasma membrane permeability （RC） , and rate of O2^- increased gradually with decreasing soil water potential, and the increasing range of the rate of O2^- was the largest. The above results suggested that P. sylvestris var. mortgolica could endure and adapt to drought stress in some extents through physiological and biochemical mechanisms, especially through increasing osmotic substances. However, the cellular tissues at the soil water potential of - 16. 18 bars were un-reversibly damaged due to the accumulation of O2^- and the aggravation of membrane lipid peroxidation.