三種不同地理分佈的田字草之葉片生理生態特徵探討

Ecophysiological Traits of Leaves of Three Marsilea Species Distributed in Different Geographical Regions

田字草（約有八十種）是兩棲性蕨類，具特殊的葉片形態及生殖構造，其分布遍及五大洲。為了探討分布在不同地理區域的三種田字草（Marsilea crenata、M. quadrifolia及M. schelpiana）其適應陸生環境的特性，我們將這三種田字草種植在相同環境下、比較陸生植株其小葉形態特徵、光學特性及光合作用表現。結果發現三種田字草小葉在某些生理生態特徵上有顯著的不同：在三者中，M. quadrifolia（分布於降雨較少的溫帶）的小葉有最高的表皮毛密度及水分使用效率；Ｍ. schelpiana（分布於有較高光照量的南非）有最長的葉柄及最大的裂葉指數、總氣孔面積指數、第二光系統電子傳遞鏈速率及光飽和光合作用速率；M. crenata（主要分布於有較高降雨量及溼度的東南亞）有最低的裂葉指數及水分使用效率。因此，這三種田字草的葉部特徵反應其棲地之氣候形態，結果也顯示水可利用度及光照量是影響這三種田字草地理分布不同的兩個重要因子。

Marsilea, an amphibian fern genus (containing ca. 80 species) characterized by their unusual leaves and reproductive structures, is distributed over the five continents. To investigate the adaptation traits of three Marsilea species (M. crenata, M. quadrifolia, and M. schelpiana), distributed in different geographic regions, to terrestrial conditions, we compared morphological features, optical properties and photosynthetic performance of leaflets of the three species grown in terrestrial environment. The results showed that leaflets of the three species had significant differences in some of the ecophysiogical traits. Among the three species, M. quadrifolia (distributed in temperate region where receiving low precipitation) had the highest trichome density on its leaflet surface and the highest water use efficiency, M. schelpiana (mainly in southern Africa where accepting high level of solar irradiance) had the tallest petiole and the highest leaf dissection index, total stomatal pore area index, PSII electron transport rate and photosaturated photosynthetic rate, M. crenata (mainly in southeastern Asia region where receiving high precipitation and with high humidity) had the lowest leaf dissection index and water use efficiency. Accordingly, leaf characteristics of the three Marsilea species reflect the climate pattern of their habitats. The results also suggest that water availability and light intensity are two of the important factors contributing to the geographic distribution of the three species.