中文摘要：

研究不同光环境对常绿阔叶林中喜树和四川大头茶幼苗生长的影响。结果表明：1）落叶阔叶树种喜树幼苗通过提高自遮荫程度、增大叶悬挂角、增加根生物量比和减小比叶面积适应旷地环境,在旷地中具有最大的相对生长速率,而常绿阔叶树种四川大头茶幼苗没有表现出对旷地光环境的良好适应;2）四川大头茶幼苗在林窗中通过增加叶片数、提高单叶面积、比叶面积和叶生物量比接受更多光能,相对于旷地和林下具有较快的高度生长,喜树幼苗比四川大头茶幼苗在林窗中具有更大的单叶面积、叶柄长度、总叶面积和总叶面积增长率;3）在3—8月,喜树在林窗中的株高增加约35.3cm,约为四川大头茶（约6.6cm）的5.3倍,喜树在林窗中具有明显的光资源竞争优势,表现出比常绿阔叶树种四川大头茶更高的相对生长速率,这就是喜树存在于常绿阔叶林的一个重要原因;4）郁闭林下的光资源有限,2个树种幼苗都不能在林下良好生长;5）喜树幼苗叶性状在不同光环境的可塑性指数远大于四川大头茶,这是喜树能够在常绿阔叶林中存在的另一重要原因。

英文摘要：

The effects of different light regimes（such as open,gap and understory） on the phonotypic plasticity of the seedlings of Camptotheca acuminata and Gordonia acuminata were studied,based on the leaf traits. The results showed that：1） Seedings of C. acuminata,as a deciduous broadleaf tree,mainly improved the self-shading,increased the midrib angle and ratio of root biomass to total biomass,and decreased the specific leaf area to adapt the full light in the open sites. Therefore those seedlings exhibited the highest relative growth rate in the open sites in compared with the other light regimes. However, the seedling of G. aeuminata did not show the similar adaptability in the open light environment. 2） In order to receive more light energy in gap, the seedlings of G. acuminata deveioped more leaves, and larger single leaf area and specific leaf area, and increased the ratio of leaf biomass to total biomass. Therefore, the seedlings of G. aeuminata could grow relatively higher in gap than that in open and understory. Compared with G. acuminata, the seedlings of C. acuminata in gap had larger single leaf area and total leaf area, longer petiole, and higher growth rates in height and total leaf area. 3） From March to August, the height of the seedlings of C. acuminata in gap increased by 35.3 cm,which was about 5.3 times of the height growth （6.6 cm） of the seedlings of G. acuminata. Therefore, in the gap, C. acuminata seedlings with a distinct competitive advantage of light resources showed a higher relative growth rate than G. acuminata, which was one of the major reasons why the deciduous broad- leaved tree of C. acuminata in evergreen broad-leaved forests. 4） Because of the lack of sufficient solar energy, the two trees＇ seedlings could not grow well in the understory. 5） The phenotypic plasticity index based on leaf traits in different light regimes of C. acuminata was much higher than the those of G. acuminata, which was another important reason for the existence of C. acuminata in evergree