| Summary: | 碩士 === 國立臺灣大學 === 生態學與演化生物學研究所 === 96 === This study investigated two varieties of Bidens pilosa which have differential distribution pattern along altitudes in Taiwan. While B. pilosa var. radiata was introduced into Taiwan in 1984 and has become an invasive plant, B. pilosa var. minor has been in Taiwan since 1928. Field observation reveals that B. pilosa var. radiata is more widely distributed than B. pilosa var. minor at lower altitudes. However, in mid altitudes, population size of B. pilosa var. minor increases while that of B. pilosa var. radiata decreases. In this study, I investigated factors affecting the differential distribution pattern of these two varieties of B. pilosa between two altitudes and tested the following hypotheses, (1) B. pilosa var. radiata has growth advantages over B. pilosa var. minor at low altitudes, (2) environmental factors limit the growth of B. pilosa var. radiata hence cause its population size to decrease in mid altitudes, and (3) populations of B. pilosa var. minor at mid altitudes have developed genetic differentiation in adaptation to mid-altitudinal environment. To test these hypotheses, I compared the responses of these two varieties grown under different irradiance and watering regimes. The growth of adventitious root and seed germination rate of two varieties at two temperatures, 30/25 ℃ (day/night temperature) and 18/13 ℃, were also examined. I also measured morphological, physiological and reproductive characteristics of these two varieties growing at low (500 m) and mid (1300~1600 m) altitudes. Finally, I transplanted these populations to a farm at National Taiwan University to compare the growth of two varieties and to examine if genetic differentiation has occurred in these populations.
When two varieties were grown in NTU farm at low altitudes, B. pilosa var. radiata had higher relative growth rate in lateral branch and longer life span than B. pilosa var. minor. In addition, B. pilosa var. radiata had higher growth rate of adventitious root than B. pilosa var. minor at high temperature. These traits may enable B. pilosa var. radiata to distribute more widely than B. pilosa var. minor at lower altitudes. Low temperature significantly reduced the growth rate of adventitious root and seed germination percentage of B. pilosa var. radiata. Therefore, low temperature is an important factor limiting the invasion of B. pilosa var. radiata into higher altitudes. Results from field measurement and transplant experiment indicate that the population of B. pilosa var. minor at mid altitudes has developed genetic differentiation in adaptation to lower temperature and lower light intensity environment.
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