FUNCTIONS OF BRANCHES OF THE CLONAL TREE SYMPLOCOS LAURINA
克隆乔木黄牛奶树枝条的功能特征

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.