中文摘要：

为探讨我国西南干热河谷这一严酷生境中植物抗氧化系统对多种胁迫因子的响应机制，以该地区最干热的元江河谷萨王纳植被中光合能力有明显差异的两个优势种——常绿的毛枝青冈（Cyclobalanopsis helferiana）和干热季落叶的三叶漆（Terminthia paniculata）为材料，研究了其抗氧化系统活性在高温雨季、干凉季和干热季的变化规律。结果表明：从总体上看两树种抗氧化系统在干凉季活性最高，然而，两树种谷胱甘肽转移酶和谷胱甘肽过氧化物酶都在随后的干热季特异表达。两树种主要非酶抗氧化物质——抗坏血酸（ASC）和谷胱甘肽库容量与水．水循环起端酶超氧化物歧化酶（SOD）活性差异不大，但光合速率低的三叶漆水．水循环和抗坏血酸．谷胱甘肽循环其它酶活性显著高于光合强的毛枝青冈。三叶漆抗氧化系统比毛枝青冈启动积极，但后者有更持久的抗氧化能力。与其它逆境中植物相比，两树种有更发达的抗氧化系统，故能始终保持相对低的丙二醛含量。

英文摘要：

Aims Hot-dry valleys in southwestern China are adverse habitats. The foliar antioxidant system of plants growing there must play an important role in protecting their photosynthetic apparatus against photo-oxidation. Our aim was to characterize the responses of the antioxidant system to seasonal changes of multiple abiotic stresses in two dominant tree species in the hot-dry valley of the Yuanjiang River, Yunnan. Methods We chose two savanna species with different photosynthetic rates for study： the evergreen Cyclobalanopsis helferiana （oak） and drought-deciduous Terminthia paniculata （sumach）. We exam- ined changes of the two main antioxidants, ascorbate （ASC） and glutathione contents and the activities of all of the antioxidant enzymes of the water-water and ASC-glutathione cycle in these two species from the hot-rainy season to the chill-dry season and to the warm-dry season. Important findings Both species showed the highest antioxidant activity in the chill-dry season; however, they had the highest activities of glutathione transferase and glutathione peroxidase in the subsequent warm-dry season. They had similar ASC and glutathione contents and activity of SOD, the initial enzyme of water-water cycle, but sumach displayed higher activities of most antioxidant enzymes in the water-water and ASC-glutathione cycles in all seasons compared to oak. Overall, sumach activated its antioxidant system more actively than oak, yet oak had more persistent antioxidant activity than sumach. Compared with activities of antioxidant systems of plants growing in other adverse conditions, the two study species have stronger antioxidant capacity, which is consistent with their absolutely lower contents of malondialdehyde in all seasons.