Comparisons of three varieties of Bidens pilosa to identify what traits make the variety radiata invasive in Taiwan
Date Issued
2014
Date
2014
Author(s)
Huang, Ya-Lun
Abstract
The invasion of exotic species has become one of the most important factors reducing biodiversity. Three varieties of Bidens pilosa: var. minor, var. pilosa and var. radiata, were listed in the Flora of Taiwan. Among the three varieties, the first record of var. radiata in Taiwan was later than those of the other two varieties. However, after being introduced into Taiwan, var. radiata has become a common weed on roadsides, uncultivated field and waste grounds from low to middle elevations in the past three decades. In order to identify what traits let var. radaita dominant over the other two varieties and become one of serious invasive plants in Taiwan lowland after its introduction, I compared the growth, breeding system and life history traits of these three varieties.
The relative growth rates of the three varieties were higher in summer than in fall. The result suggested that summer with high light and temperature was more suitable for the growth of all three varieties than fall. In summer, var. radaita grew faster and accumulated more biomass than the other two varieties. Thus, var. radaita had growth advantage over the other two varieties in regions with high light and high temperature conditions. In addition, var. radaita had higher root/biomass ratio, more horizontally oriented lateral shoots, and grew more adventitious roots than the other two varieties. Among the three varieties, only var. radiata had secondary axillary shoots. With these characters, var. radiata had a greater potential of vegetative reproduction than the other two varieties.
It was found that all three varieties had secondary pollen presentation and were incompletely protandrous. However, when these three varieties grew sympatrically in a greenhouse, var. minor and var. pilosa produced achenes while var. radiata had no achene set. Bagging experiments were conducted to explain the phenomenon. From the results of bagging treatment, I confirmed that self-incompatibility was the key mechanism preventing selfing in var. radiata, while var. minor and var. pilosa were self-compatible and were capable of producing achenes in bags by selfing. Significant differences were found in many traits among individuals of var. radiata. The result indicated that high heterogeneities in many traits of var. raidata might result from its obligate xenogamous breeding system.
Although var. radiata flowered later and set less achenes than the other two varieties, half individuals of var. radiata lived longer and formed ramets by vegetative reproduction. These ramets flowered and set achenes when matured. Consequently, var. radiata accumulated significantly more achenes than the other two varieties after being planted for one year. In addition, although achenes of var. minor and var. pilosa were heavier and germinated earlier than those of var. radiata, the final germination percentage was not different among the three varieties. Having more and lighter achenes, var. radiata would be dispersed by animals more easily than the other two varieties.
In conclusion, massive achenes produced by sexual reproduction potentially allow var. radiata dispersing into far-reaching habitats. High heterogeneities were found in many traits of var. radiata, which might allow var. radiata to have widely fundamental niche. After established in a new habitat, var. radiata could generate many ramets by vegetative reproduction, expand horizontally, eventually occupied the area and became dominant. In summary, the breeding system and life history traits of var. radiata, in combination with the warm and high light climate and land use change in Taiwan confer var. radiata advantage over var. minor and var. pilosa and become one of serious invasive plants in Taiwan.
Subjects
繁育系統
生長
大花咸豐草
入侵植物
生活史特徵
Type
thesis
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