四種入侵性不同的豆科野百合屬歸化植物之生理特徵比較

Abstract

入侵性(invasiveness)指外來物種進入非其原生地後，在當地擴散並建立族群的能力。過去的研究顯示，臺灣豆科野百合屬(Crotalaria)四種歸化植物：南美豬屎豆(Crotalaria zanzibarica Benth)、黃野百合(C. pallida Ait. var. obovata (G. Don) Polhill)、黃豬屎豆(C. micans Link)和恆春野百合(C. incana L.)，其入侵性的強弱顯著不同：南美豬屎豆(Cz)＞黃野百合(Cp)＞黃豬屎豆(Cm)＞恆春野百合(Ci)。 本研究採收該四種野外生長的野百合屬植物的種子，進行溫室實驗以比較並分析這些同屬的外來植物其生理、形態、繁殖等特徵差異，討論這些生物特徵與其入侵性的相關性，以期找出影響入侵性強弱表現的生物特徵。 本研究提出下列假說來檢驗這四種野百合屬歸化植物的生長及生理特性：入侵性較強的物種(1)其種子可在較廣的溫度範圍和較廣的土壤深度條件下發芽；(2) 其種子小苗相對生長速率較快；(3)擁有較多的葉片數量、葉面積；(4)總生物量(biomass)值較高，也會將較多的生物量投資在葉片部位；(5)有較高的植株高度；(6)單位葉片面積擁有較高的最大光合作用速率。 結果顯示這四種野百合屬歸化植物生理和生長特性與入侵性強弱趨勢如下：在發芽試驗結果中，最適合發芽(＞50％發芽率)的土壤深度範圍依序為恆春野百合(Ci)＞黃野百合(Cp)＝南美豬屎豆(Cz)＞黃豬屎豆(Cm)，與入侵性不相符；最適發芽溫度範圍大小依序為南美豬屎豆(Cz)＝黃野百合(Cp)＝恆春野百合(Ci)＞黃豬屎豆(Cm)，也不符合先前預測的入侵性。在小苗生長速率與入侵性方面，發現葉片數量與小苗相對生長速率相關，但並不符合入侵性趨勢。成熟植株的生物量及葉片生物量，以及總葉片面積趨勢與入侵性相符。葉片特徵部分在單位乾重葉面積指數、水含量比例以及總氣孔密度上種間有顯著差異但與入侵性趨勢不相符；葉片單位面積的光合作用能力趨勢與入侵性趨勢也不符。 綜合上述，三個月成熟植株總生物量，葉片生物量以及植株葉片總面積與入侵性趨勢相符。結果支持上述第(3)及(4)的假設。Invasiveness is the ability of alien plants to spread beyond their introduced sites and become established in new locations. It has been shown that invasiveness is usually determined by reproductive, morphological, physiological traits and growth strategies. Previous studies have shown that four introduced Crotalaria spp., Crotalaria zanzibarica Benth, C. pallida Ait. var obovata,C. micans Link, and C. incana L., in Taiwan have siginificant difference in invasiveness. The order of the invasiveness is C. zanzibarica ＞C. pallida＞C. micans＞C. incana. To invegestigate the factors contributing to the invasiveness of the four species, I collected seeds of the four species and germinated them in greenhouse. I approached the invasiveness by comparing seed germination plasticity, seedling relative growth rate, total biomass and biomass allocation of adult plants, and photosynthesis capacity of the four Crotalaria congeners. I proposed following hypotheses to test the relationship between measured traits and invasiveness, species with higher invasiveness：(1) can germinate under wider temperature ranges and soil depth conditions；(2) have higher relative growth rate at seedling stage；(3) have more leaves per plant；(4) accumulate more biomass and allocate more biomass to leaves；(5) grow taller, and (6) have higher maximum photosynthetic rate per unit leaf area. The results showed that the trend of the seed germination traits, the seedling relative growth rate, and leaf photosynthetic traits of the four species were not consistent with their invasiveness of the four species. Among the traits invegestigated, the total biomass accumulated, leaf biomass and total leaf area, in plants of three month old were the best indicators of the invasiveness. The results support the hypotheses (3) and (4). Accordingly, I concluded whole plant biomass and leaf biomass were the most important factors contributing to these congeners’ invasiveness.