天台山云锦杜鹃幼树的构型分析

Architectural analysis of Rhododendron fortunei saplings in Mountain Tiantai,Zhejiang Province

在浙江天台华顶山，云锦杜鹃Rhododendron fortunei生长于多种林分中。对生活在落叶阔叶林林隙内和林缘灌草丛中的云锦杜鹃幼树（树高80～130cm）的构型进行了统计分析。结果显示：①林隙内的幼树树冠窄小，枝倾角较大，分枝相对较长，但分枝率相对较低，尤其是植株下层的枝条差别更大。说明在光照条件差的生境中，幼树的高生长显著，从而可尽快摆脱光胁迫的制约。②林隙内的幼树叶倾角相对较小，尤其是下层枝条的叶片部分比较平展，这可能有利于接受更多的散射光；而枝径比以及枝、叶的方位角等未发生显著的变化。另外，幼树的各级分枝均以单轴分枝为主，但顶端优势不甚明显，使树冠具有合轴分枝的形态特征。由此可见，云锦杜鹃的分枝特征具有相对稳定性，但枝长、分枝率、枝倾角和叶倾角等对生境的光照比较敏感，且枝长与分枝率间存在着一定的交换。

Rhododendron fortunei lives in many kinds of forests in Mountain Tiantai （29°15′ N, 121°06′ E）. Comparative analysis has been made on the architecture of R. fortunei saplings in the canopy gap of defoliated broad-leaved forest and in scrubs edge of the forest. The results showed that saplings in the canopy gap had thinner and narrower crown with longer branch, wider branch angle to horizon, lower bifurcation ratio and leaf angle to horizon, in comparison with those in the scrubs. All the differences were especially noticeable in the undergrowth. This indicated that the saplings would spread their leaves to receive more sunlight. Saplings had a low angle of leaves, and the leaves were smaller than those of the petiole, which made it possible for them to receive more scattered light. And the ratio of branch diameter, azimuths of branch and leaves had no significant difference. In addition, saplings mainly adopted monopodial branching, and the apical dominance was not evident. So the crown was characterized by sympodial branching in the canopy gap. It followed that the character of ramification of the R. fortunei had the relative stability, but in the two different habitats, bifurcation ratio, branch length, the angle of branch and leaf all varied significantly, and there was a certain tradeoff between the length of branch and the bifurcation ratio. [Ch, 1 fig. 4 tab. 20 ref. ]