中文摘要：

通过野外取样，对黄土丘陵沟壑区坡沟系统5种立地环境（阳坡沟谷地和沟间地、峁顶、阴坡沟间地和沟谷地）下19种主要物种叶片的膜脂过氧化指标丙二醛（MDA）含量，3种抗氧化酶即超氧化物歧化酶（SOD）、过氧化物酶（POD）和过氧化氢酶（CAT）活性，及2种非酶抗氧化物质即还原型谷胱甘肽（GSH）和类胡萝卜素（Car）含量进行了测定与分析，旨在探讨不同物种适应不同立地环境的抗氧化特性。结果表明：各立地环境下物种间的 MDA积累量均呈极显著差异（P＜0．01），说明各立地环境的胁迫均导致供试物种遭受不同程度的膜脂过氧化作用，其中互生叶醉鱼草的膜脂过氧化水平最高，猪毛蒿的最低；在不同立地环境间，白羊草、达乌里胡枝子、阿尔泰狗娃花和狼牙刺的各抗氧化酶活性和非酶抗氧化物质含量均无显著差异（P＞0．05），中华隐子草、糙隐子草、长芒草、草木樨状黄芪、糙叶黄芪、甘草、菊叶委陵菜、猪毛蒿、铁杆蒿、茭蒿、沙棘、杠柳和互生叶醉鱼草存在显著（P＜0．05）或极显著（P＜0．01）差异，说明在不同立地环境下，前者均采用多种抗氧化酶和非酶抗氧化物质协同抵御胁迫的策略，后者则调用不同抗氧化酶或非酶抗氧化物质发挥主要抵御作用；由于植物科属和碳同化途径的差异，其抗氧化特性也存在差异：菊科和豆科植物分别主要通过CAT和SOD减轻活性氧的伤害，禾本科植物则能以较高的SOD、POD活性和Car含量维持较低的膜脂过氧化水平，C4植物比C3植物具有较高的GSH 和Car含量。隶属函数法综合评价表明，中华隐子草的抗氧化能力最强，互生叶醉鱼草的最弱。

英文摘要：

This study investigated antioxidant properties of main plant species on 5 different site classes (sunny or shady gully and inter-gully land or hilltops))in the hilly-gullied Loess Plateau.From field sampling,the ac-tivities of the antioxidant enzymes-superoxide dismutase (SOD),peroxidase (POD)and catalase (CAT),the contents of two non-enzymatic antioxidants-reduced glutathione (GSH)and carotenoid (Car),and the malondi-aldehyde (MDA )levels of leaf tissues of nineteen species were determined.There were highly significant differences in MDA accumulation among species on each site (P<0.01).This indicated that the test species suffered varying degrees of membrane lipid peroxidation,with Buddlejaalternifolia and Artemisiascoparia being highest and lowest respectively.There were significant differences in antioxidant enzyme activity or non-enzymatic antioxidant levels among sites for each test species,except for Bothriochloaischcemum,Lespedeza davurica,Heteropappusaltaicusand Sophoradavidii,which suggests that these four species possessed up-regulation of antioxidant enzymes and non-enzymatic antioxidant synthesis regardless of different site stresses, while Cleistogeneschinensis,Cleistogenessquarrosa,Stipabungeana,Astragalusmelilotoides,Astragalus scaberrimus,Glycyrrhizauralensis,Potentillatanacetifolia,A.scoparia,Artemisiavestita,Artemisiagi-raldii,Hippophaerhamnoides,Periplocasepium and B.alternifoliaregulated their antioxidant enzymes or non-enzymatic antioxidant levels.From the botanical family perspective,antioxidant properties of the test spe-cies were distinct.CAT and SOD were respectively produced by five composite and five leguminous plant spe-cies to reduce damage from reactive oxygen species.Four graminaceous plants were able to attain high SOD, POD activities and Car contents to maintain a low level of membrane lipid peroxidation.Because of different carbon assimilation pathways,antioxidant properties of the test species were also distinct.In particular,C4 plants had higher GSH and Car contents than C3 pla