Aiba Masahiro, Nakashizuka Tohru
Center for Ecological Research, Kyoto University, Hirano, Otsu 520-2113, Japan.
Ann Bot. 2005 Aug;96(2):313-21. doi: 10.1093/aob/mci179. Epub 2005 Jun 8.
Inevitable trade-offs in structure may be a basis for differentiation in plant strategies. Juvenile trees in different functional groups are characterized by specific suites of structural traits such as crown architecture and biomass distribution. The relationship between juvenile tree structure and function was tested to find out if it is robust among functionally and taxonomically similar species of the genus Shorea that coexist sympatrically in a tropical rain forest in Borneo.
The sapling structures of 18 species were compared for standardized dry masses of 5 and 30 g. Pairwise simple correlation and multiple correlation patterns among structural traits of juveniles (0.1-1.5 m in height) of 18 Shorea species were examined using Pearson's correlation and principal component analysis (PCA), respectively. The correlation was then tested between the PCA results and three indices of shade tolerance: the net photosynthetic rate, the wood density of mature trees and seed size.
The structural variation in saplings of the genus Shorea was as large as that found in sets of species with much more diverse origins. The PCA showed that both crown architecture and allocation to leaves are major sources of variation in the structures of the 18 species investigated. Of these two axes, allocation to leaves was significantly correlated with wood density and showed a limited correlation with photosynthetic rate, whereas crown architecture was significantly correlated to seed size.
Overall, the results suggest that an allocation trade-off between leaves and other organs, which co-varied with wood density and to a certain extent with photosynthetic capacity, accounts for the difference in shade tolerance among congeneric, functionally similar species. In contrast, the relationship between the architecture and regeneration strategy differed from the pattern found between functional groups, and the function of crown architecture was ambiguous.
结构上不可避免的权衡可能是植物策略分化的基础。不同功能组的幼树具有特定的一系列结构特征，如树冠结构和生物量分布。对幼树结构与功能之间的关系进行了测试，以查明在婆罗洲热带雨林中共存的龙脑香属功能和分类相似的物种中，这种关系是否稳固。
比较了18个物种5克和30克标准化干质量的树苗结构。分别使用皮尔逊相关性和主成分分析（PCA）研究了18种龙脑香属幼树（高度0.1 - 1.5米）结构特征之间的成对简单相关性和多重相关性模式。然后测试了PCA结果与三个耐荫性指标之间的相关性：净光合速率、成熟树木的木材密度和种子大小。
龙脑香属树苗的结构变异与来源更为多样的物种组中的变异一样大。PCA表明，树冠结构和叶片分配都是所研究的18个物种结构变异的主要来源。在这两个轴中，叶片分配与木材密度显著相关，与光合速率的相关性有限，而树冠结构与种子大小显著相关。
总体而言，结果表明叶片与其他器官之间的分配权衡，与木材密度共同变化，并在一定程度上与光合能力共同变化，这解释了同属、功能相似物种之间耐荫性的差异。相比之下，结构与再生策略之间的关系与功能组之间的模式不同，树冠结构的功能尚不明确。
