| Summary: | 碩士 === 國立臺灣大學 === 生態學與演化生物學研究所 === 94 === Invasion of exotic plants is a global phenomenon which often has highly impact on the environment and economics. Bidens pilosa L. var. radiata Sch. Bip., a common weed in lowland Taiwan, is listed as one of the twenty most noxious invasive plants in Taiwan. Thus, it is important to study the invasiveness of this weed. Bidens. pilosa var. radiata is found growing closely with Bidens bipinnata L., a naturalized species, and dominates an abandoned farm in Madou Town, Tainan County, Taiwan. Taking the advantage, I compared physiological, morphological and life history traits of these two species aiming to understand possible traits contributing to the invasiveness of B. pilosa var. radiata. I tested the current hypotheses regarding the superiority of invasive plants. Accordingly, B. pilosa var. radiata is expected to have (1) life history traits and growth strategies better adapted to the local environment than B. bipinnata, (2) higher phenotypic plasticity than B. bipinnata and (3) allelopathic potential that inhibits growth of B. bipinnata. Photosynthetic measurements of field plants and plants subjected to different water treatments in greenhouse reveal that the two species had similar photosaturated photosynthetic rate and potential quantum yield of PSII. However, under the winter temperature condition of 18 ℃, B. pilosa var. radiata perfomed better in germination and photosynthesis than B. bipinnata. Thus, B. pilosa var. radiata could have advantage over B. bipinnata in winter. Compared to B. bipinnata, B. pilosa var. radiata has a later onset of flowering and better ability for vegetative reproduction, allocates more resource to leaf, and has higher lateral branch ratio, thus could accumulate more energy for longer growth period. Stem anatomy reveals that B. pilosa var. radiata could have a life span of more than one year. It appears that the two species use different life history strategies. In addition, B. pilosa var. radiata has allelopathic potential that inhibits germination and growth of B. bipinnata. The differences in these traits between the two may explain why B. pilosa var. radiata outcompetes B. bipinnata in the experimental farm and may also account for its invasive success in Taiwan.
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