浙江天童国家森林公园5种常绿阔叶植物的一次和二次抽枝进程

中国东部亚热带常绿阔叶林中, 部分常绿木本物种具有明显的二次抽枝现象, 即在春天完成第一次抽枝, 间隔一定的时间后又开始新一轮抽枝。但是关于这些植物第二次抽枝的进程, 迄今鲜有报道, 限制了人们对这些植物生活史对策的理解。该文以浙江天童常绿阔叶林中有二次抽枝的5种植物光叶山矾(Symplocos lancifolia)、檵木(Loropetalum chinense)、窄基红褐柃(Eurya rubiginosa var. attenuata)、杨梅(Myrica rubra)和栲树(Castanopsis fargesii)为研究对象, 调查并比较了第一次抽枝和第二次抽枝在昆虫取食压力、展叶动态和小枝投资大小3个方面的差异, 探讨第二次抽枝动态的主要特点。结果表明: 1)昆虫取食压力上, 杨梅、栲树2种植物第二次抽枝的叶片虫食率显著高于第一次抽枝, 光叶山矾、檵木和窄基红褐柃3种植物第一、二次抽枝的叶片虫食率没有差异; 2)在现叶速率(叶片数量的增加速率)上, 同一物种第一、二次抽枝的叶片数量增长模式相同, 光叶山矾、檵木、窄基红褐柃和杨梅4个物种呈持续式增长, 栲树则呈爆发式增长, 但是完成现叶所需时间并不完全相同, 光叶山矾、窄基红褐柃和杨梅第二次抽枝完成现叶比第一次少6-9天, 檵木和栲树第一、二次抽枝完成现叶所需时间则无差异; 3)在展叶速率上, 光叶山矾、檵木和窄基红褐柃第二次抽枝显著高于第一次抽枝, 但第一次抽枝较晚的杨梅和栲树第一、二次抽枝之间没有差异; 4)调查的5种植物, 第二次抽枝的投资总量均小于第一次抽枝, 光叶山矾、窄基红褐柃、杨梅和栲树4种植物, 第二次抽枝形成的小枝在叶片数量、单叶面积、小枝长度和小枝直径上都显著小于第一次抽枝, 檵木第二次抽枝形成的小枝在叶片数量和小枝长度上没有差异, 单叶面积和小枝直径则显著小于第一次抽枝。总体上看, 所研究物种第二次抽枝中的叶片虫食率、现叶速率和展叶速率都不小于第一次抽枝, 而第二次抽枝小枝投资总量较小, 这些可能是物种对相对较大的昆虫取食压力和即将来临的冬天不利条件等的适应。

First and second sets of shoots in five evergreen woody species from Tiantong National Forest Park of Zhejiang, China

Aims Some woody species of subtropical evergreen broad-leaved forests in Eastern China form a second set of shoots in late summer or autumn after a first set in spring. Our objective is to elucidate features of this second set of shoots, including their adaptive significance.
Methods We investigated differences between the first and second sets of shoots for five evergreen woody species (Symplocos lancifolia, Loropetalum chinense, Eurya rubiginosa var. attenuata, Myrica rubra, and Castanopsis fargesii) from an evergreen broad-leaved forest in Tiantong National Forest Park of Zhejiang, China. Herbivore damage of leaves was estimated, leaf emergence rate, leaf expansion rate and duration were calculated, and twig investment (leaf number and individual leaf area within twigs, twig stem length and diameter) was measured for both sets of shoots.
Important findings Leaves of M. rubra and C. fargesii suffered greater herbivore damage to the second shoots compared with the first, and no significant difference was found in damage between the two sets of shoots for S. lancifolia, L. chinense and E. rubiginosa var. attenuata. The first and second sets of shoots shared the same leaf emergence pattern. Symplocos lancifolia, L. chinense, E. rubiginosa var. attenuata, and M. rubra showed a succeeding type of leaf emergence, and C. fargesii showed a flushing type of leaf emergence. However, duration of leaf emergence was much shorter in the second set of shoots for S. lancifolia, E. rubiginosa var. attenuata and M. rubra than in the first but not for the other two species. Leaf expansion rate was significantly higher for the second set of shoots for S. lancifolia, L. chinense and E. rubiginosa var. attenuata and was indistinguishable for M. rubra, C. fargesii leafed out late in the first set of shoots. Moreover, leaf number (except for L. chinense), individual leaf area, twig stem length (except for L. chinense) and diameter were significantly smaller in the second than in the first set of shoots for four species, indicating lower twig investment in the second shoots for all the sampled species. In general, leaf herbivory damage, rates of leaf emergence and expansion were not smaller (sometimes significantly greater), but the total investment on twigs was significantly lower in the second shoots compared to the first. We speculate that these differences might result from the selective force of heavy herbivory pressure and adverse climate conditions of coming winter for the leaves produced during the second set of shoots.