克隆乔木黄牛奶树枝条的功能特征

 黄牛奶树(Symplocos laurina)是一种乔木克隆植物，其枝担负着支撑叶进行光合作用和克隆苗繁殖两种功能。由于枝功能的特异性在形态上表现出独特的特征：上部的枝生长比较旺盛，主要进行光合作用负责整个植株的碳水化合物供应与积累；下部的枝在形态上有所变化，基部细长而端部较基部明显增粗，并下垂呈“V”状，在生长过程中增长明显而无明显增粗现象，主要进行克隆繁殖。黄牛奶树的枝在由营养功能转变为繁殖功能的过程中年萌发次数显著增加； 枝分化成克隆苗后在截取光能方面采取了不同的策略：克隆苗作为一个新的生命体，主要通过增加叶量占据更大的水平空间来增大总叶面积以截取更多阳光，不同于营养枝通过增加单叶面积占据更大的垂直空间来增大总叶面积以截取更多阳光的方式，但在不同的生境下对照枝与压枝克隆苗达到的总叶面积却无显著差异；从各构件的生物量特征看， 对照枝的生物量主要分配在叶和叶柄等光合构件上，而枝分化成克隆苗后生物量主要分配在茎上。即黄牛奶树的枝随着着地后功能的变化，在形态等各方面都有相应的变化，这可能是由于功能变化后内源激素发生变化的结果，但这有待于进一步研究。

FUNCTIONS OF BRANCHES OF THE CLONAL TREE SYMPLOCOS LAURINA

Symplocos laurina is an arboreal clonal plant. Its branches are bi-functional organs that both undertake photosynthesis and produce ramets for propagation. Due to their unique functions, the branches of S. laurina differ in their physical appearance: upper branches grow well and rather strong and function to accumulate and provide photosynthates to the whole plant, whereas the lower branches have slim proximal ends but much sturdier head ends and grow downward in a V shape. Lower branches grow in length rather than in diameter to clone younger ramets. When branches switch their roles from photosynthetic structures to ramet producers, they experience much greater germination. Apical dominance and stimulation from root appearance may be the two primary reasons. Germination times are very different between ramets in different habitats but do not differ in control branches indicating that older and stronger trees are not as sensitive as the younger tender ramets to environmental conditions, even though the ramets are still connected to the mother plant. As new organisms, young ramets adopt different strategies to compete for light: they grow hard to increase the number of leaves so as to enlarge the total light-receiving area in horizontal space. In contrast, parent branches increase the area of each leaf to get the largest possible leaf area in vertical space. Because the ramets can germinate more than once a year, they can produce more leaves than their parent branches, which can only germinate once and the number of leaves are predetermined by the buds. However, even in different habitats, no significant differences in total leaf area were observed between ramet-produced branches and control branches. The biomass of leaves, petioles and the total biomass of plant change greatly among habitats, but they don't change with the role switch of the branches as ramets producers. Stem biomass does not respond to different habitats but the role switch of branches does affect stem biomass. Control branches allocate their biomass mainly to photosynthesis modules, such as leaves and petioles; in contrast ramets focus most their biomass on stems. We conclude that branches change their function after they take root in the ground, which brings about correspondent changes in their morphological features. This is probably due to internal hormonal changes as a branch changes its function but more research is needed to better understand this phenomenon.