中文摘要：

以广西猫儿山高海拔常绿针阔叶混交林中的两个优势树种南方铁杉和褐叶青冈为研究材料,测定二者在不同季节的光合色素、光合速率、叶绿素荧光和抗氧化系统等特征,探讨并比较了冬季低温气候条件下这两种常绿越冬树种的光合作用和抗氧化防御策略的差异。在冬季胁迫下,南方铁杉和褐叶青冈向下调整叶绿素（Chl）含量、凌晨光系统Ⅱ潜在最大光化学效率（Fv/Fm-predawn）、净光合速率（Amax）和气孔导度（Gs）到最小值。褐叶青冈叶片3种主要保护酶超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）活性和2种抗氧化物质抗坏血酸（As A）、谷胱甘肽（GSH）以及光保护色素类萝卜素（Car）含量在冬季最高,它们在清除活性氧、抵御外界不良环境协同性强;而南方铁杉叶片仅有As A、GSH和Car保持着协同作用以应对冬季胁迫。南方铁杉和褐叶青冈叶片的MDA含量的季节变化除了与外界环境条件的变化有关外,还与抗氧化酶活性及抗氧化剂的积累密切相关。综上所述,南方铁杉和褐叶青冈对冬季的适应采取不同的抗氧化防御策略,但冬季光合适应策略均采用了下调策略。

英文摘要：

We selected two dominant tree species including Tsuga chinensis and Cyclobalanopsis stewardiana grown in the evergreen needle-leaved and broad-leaved mixed forest at high-altitude on Mao＇er Mountain,and studied their seasonal changes in photosynthetic pigments, net photosynthetic rate（ Amax）, chlorophyll fluorescence and antioxidative system. T. chinensis and C. stewardiana down-regulated the values of chlorophyll（ Chl） content,predawn maximum photochemistry efficiency of PS Ⅱ（ Fv/ Fm-predawn）,Amaxand stomatal conductance（ Gs） to the minimum during winter stress. The activities of superoxide dismutase（ SOD）,peroxidase（ POD）, catalase（ CAT） and the contents of ascorbic acid（ As A）, glutathione（ GSH） and carotenoids（ Car） of C. stewardiana were the highest in winter,which showed good synergy in resisting adverse external environments and scavenging reactive oxygen species（ ROS）,while only As A,GSH and Car in T.chinensis maintained good synergy in resisting winter stress. The seasonal changes of MDA contents in T.chinensis and C. stewardiana were correlated with the seasonal variations of environment as well as the seasonal variations of antioxidative enzyme activities and antioxidants accumulation. Therefore,T. chinensis and C.stewardiana had different antioxidant-defense strategies,but the same photosynthetic adaptation strategy was down regulation for winter acclimation.