三種田字草生理生態特徵探討

Studies on ecophysiological traits of three Marsilea species

吳泰中(Tai-Chung Wu)

指導教授 ： 高文媛

國立臺灣大學/生命科學院/生態學與演化生物學研究所/博士(2020年)

https://doi.org/10.6342/NTU202000621

摘要

植物生理生態學研究植物與環境之間的相互作用，目的在探討環境因子如何影響植物的分佈，並藉由植物生理生態特徵推測了解以前的氣候變化及追蹤植物的演化。
田字草是蘋科(Marsileaceae)的兩棲性蕨類，約有65種，廣泛分佈世界不同地理區域。田字草的葉子不同於其他蕨類植物，具有十字形排列的四片小葉。其葉片形態會隨環境因子而改變。植株在沈水生長時，小葉全緣或具細齒狀葉緣；但在挺水生長時，小葉呈現全緣、鋸齒狀或裂葉。本文研究田字草葉片和環境因子間的關係，目的在了解其如何適應環境變化及其分佈。
比較葉片形態不同、且分佈於不同地理區域的三種田字草後，發現其葉片形態和光合作用生理反映其地理分佈的環境因子：在這三個物種中，主要分布於南非的M. schelpiana具有最高的裂葉指數，總氣孔面積指數，第二光系統電子傳輸鍊速率和光飽和光合作用速率，因此是適應強光的植物；而主要分佈在東南亞溫暖濕潤區域的M. crenata，其裂葉指數和水分利用效率最低；而主要分布在溫帶地區的M. quadrifolia其葉片光合能力與M. crenata相似，但光合作用水分利用效率顯著高於M. crenata。相較於其他兩種田字草，M .quadrifolia小葉表面具顯著較多的表皮毛，因此接著探討Ｍ. quadrifolia表皮毛的功能，結果發現：在水份充足下生長的M. quadrifolia比在乾旱逆境下生長的植株其小葉具有顯著較多的表皮毛；測量去除表皮毛前和去除表皮毛後葉片光學特性、光合作用第二光系統活性及蒸散作用後，結果顯示：Ｍ. quadrifolia葉表皮毛的主要功能在減少水分喪失。
測量M. crenata的光合作用氣體交換反應後，發現M. crenata的氣孔會隨空氣中二氧化碳濃度升高和添加離層酸而降低，其氣孔也具有藍光誘導的特定氣孔反應。又相較於全光照下生長的植株，生長於遮陰環境的M. crenata其葉片氣孔對於二氧化碳濃度增加以及藍光誘導有顯著較低的反應。結果顯示M. crenata具有主動調節機制，但此主動調節機制能力會受生長環境影響。
依據實驗結果，本論文推論田字草具高度的表型可塑性及多樣的生理生態特徵，因此可以適應多樣的環境及廣泛分佈於世界不同地理區域。

關鍵字

田字草 ； 裂葉指數 ； 總氣孔面積指數 ； 第二光系統葉綠素螢光 ； 光合作用氣體交換指數 ； 表皮毛 ； 光學特性 ； 主動氣孔調節 ； 二氧化碳 ； 離層酸 ； 藍光特定氣孔反應

並列摘要

Studying the interactions between plants and environment is an important subject in plant physiology and ecology. The knowledge gained from these studies will help in projecting how plants adapt to global climate change and in tracing plant evolution in the past.
Marsilea, a genus of approximately 65 species of aquatic ferns belonging to the family of Marsileaceae, has a cosmopolitan distribution but is sparsely distributed in cool-temperate regions and oceanic islands. Leaves of Marsilea are distinct from all other ferns, comprising a petiole terminated by four leaflets in a cruciform arrangement. The leaf morphology of Marsilea varies with environmental conditions. For example, in submerged plants, the leaflets are entire to crenulate, whereas the leaflets are crenate to lobed in emergent plants. The objectives of this thesis are to investigate how leaf morphological variation can help Marsilea surviving in different environments and how Marsilea adapts (or acclimates) to changes in the environmental condition.
In this study, I studied three Marsilea species with distinct geographical distribution: M. quadrifolia ( mainly distributed in the temperate region), M. crenata (mainly distributed in southeastern Asia), and M. schelpiana (mainly distributed in southern African). Among the three species, M. schelpiana had the highest leaf dissection index, total stomatal pore area index, PSII electron transport rate, and photosaturated photosynthetic rate, which were considered as characteristics of sun-adapted plants. M. crenata, distributed in warm and humid environments, had the lowest leaf dissection index and water use efficiency. Although M. quadrifolia had similar photosynthetic capacity with M. crenata, the water use efficiency of M. quadrifolia was significantly higher than that of M. crenata. Accordingly, their leaf morphology and photosynthetic physiology reflect the environment condition of their geographical distribution. I also found that leaves of M. quadrifolia grown under low water availability produced more trichomes than those under high water availability. The results of the measurements of the optical property and photosynthetic performance between intact and de-trichomed leaves of M. quadrifolia indicate that the presence of trichomes is of more importance in reducing water loss than in reflecting light and protecting leaves against the potentially damaging effect of photoinhibition in aerial environment.
Some previous studies indicated that the active stomatal regulation (responding to CO2, abscisic acid (ABA), and blue light) is absent in the early evolved vascular plants, including fern and lycophyte. In this study, I found that the stomata of M. crenata did respond to the variation of CO2, and exogenous application of ABA. However, the shade-grown plants of M. crenata showed less degree of response capacity than those grown under full light. I also confirmed that not all the ferns of Polypodiopsida lack the specific stomatal opening response induced by blue light. Marsilea crenata grown under shade condition had also lost the specific response. Therefore, fern species and growth conditions should be taken into account when mapping the evolution of stomatal response of land plants.

並列關鍵字

Marsilea ； leaf dissection index ； total stomatal pore area index ； PSII chlorophyll fluorescence ； photosynthetic gas exchanged parameters ； trichome ； optical property ； active stomatal behavior ； CO2 ； abscisic acid ； blue-light specific stomatal response

參考文獻

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