中文摘要：

以祁连山寺大隆林区连续海拔梯度（2665～3365m）上青海云杉（Piceacrassifolia）和祁连圆柏（Sabinapmewalskii）为材料，测定叶片中抗氧化保护系统的变化，探讨常绿木本植物抗氧化系统对高山极端环境的适应机制。结果显示，祁连圆柏和青海云杉叶片中丙二醛（MDA）含量均与海拔高度呈正相关，相同海拔上青海云杉MDA含量极显著高于祁连圆柏（P〈0．01）。随海拔升高，两树种抗氧化保护酶超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）、抗坏血酸过氧化物酶（APX）、谷胱甘肽还原酶（GR）活性和非酶促抗氧化剂脯氨酸（Pro）、抗坏血酸（AsA）、还原性谷胱甘肽（GSH）含量均呈明显增加趋势。青海云杉叶片的AsA水平高于祁连圆柏，但对海拔变化的敏感性较低；祁连圆柏的GSH、Pro水平及其对海拔变化的敏感性均高于青海云杉。结果表明，研究区青海云杉所受过氧化伤害较祁连圆柏更严重，但两树种清除O2的能力相当而主要负责分解H2O2的酶种有所不同：祁连圆柏中为POD，青海云杉中则为CAT、APX和GR，AsA-GSH循环系统在青海云杉活性氧清除中的作用强于在祁连圆柏中，祁连圆柏的活性氧清除物质可能以Pro为主。

英文摘要：

Aims The antioxidative defense capacity of plants plays an important role in extreme environments. We investigated the antioxidative system in Picea crassifolia and Sabina przewalskii leaves along an altitudinal gradient in Sidalong forests of Qilian Mountains to study the response of antioxidative systems in evergreen xylophytes to subalpine environment. Methods We determined the contents of malonaldehyde （MDA）, praline （Pro）, ascorbic acid （AsA） and glutathione （GSH）, as well as the activities of superoxide dismutase （SOD）, peroxidase （POD）, catalase （CAT）, ascorbate peroxidase （APX） and glutathione reductase （GR） in leaves of P. crassifolia and S. przewalskii from different altitudes （2 665-3 365 m）. Important findings The MDA contents in P. crassifolia and S. przewalskii leaves positively and sig- nificantly correlated with altitude. At the same altitude, the MDA content in S. przewalskii leaves was significantly higher than that in P. crassifolia leaves. With increasing altitude, the content of Pro, AsA and GSH and the activities of SOD, POD, CAT, APX and GR in leaves of both P. crassifolia and S. przewalsldi increased. The sensitivity of AsA, GSH and Pro in S. przewalskii leaves along the altitudinal gradient was higher than those in P. crassifolia, although the AsA content was lower than the later. Those results suggested that S. przewalskii suffered greater oxidative stress than P. crassifolia, but its capacity to cavenge O2- was similar. POD was a main enzyme in S. przewalsldi as decomposing H2O2, but P. crassifolia was CAT, APX and GR. The action of AsA-GSH circulatory system in P. crassifolia was greater than that in S. przewalskii, and Pro was the most important antioxidant substance in S.przewalskii.