兩種附生蕨類可孕性葉及非孕性葉的生理生態比較研究

Abstract

植物的能量有限，在各種作用如繁殖、生長、光合作用等之間常要有所權衡。蕨類繁殖主要透過孢子，產生孢子可能對蕨類行光合作用等重要生理作用有所影響，但至今相關研究仍少。部分蕨類有二型葉，其中一型葉會產生孢子，稱作可孕性葉；另一型不會孕育出孢子，稱為非孕性葉。先前針對蕨類二型葉之研究多聚焦在地生蕨類，且研究對象之可孕性葉葉背幾乎被孢子囊堆佔滿，光合作用效率顯著低於非孕性葉。但因蕨類有豐富的葉型及生長形式，先前研究只涵蓋到很少部分的蕨類，因此所得結果之普遍性尚難確立。本研究檢驗福山試驗林伏石蕨及柳葉劍蕨兩種有著二型葉之附生蕨類，探討兩種葉型間物候、生理生態、形態特徵差異，包括光合作用效率、氣孔密度、滲透潛勢、葉綠素濃度等，試圖了解他們在繁殖、光合作用等之間的權衡及調適。研究結果兩種蕨類的非孕性葉和可孕性葉的光合作用速率、滲透勢能、葉綠素濃度都沒有顯著差異，而可孕性葉的氣孔密度顯著高於非孕性葉，柳葉劍蕨另測量了氣孔導度及細胞內二氧化碳濃度，在兩種葉片間也無顯著差異。結合過往研究推論，可孕性葉的葉面積、被孢子囊堆遮蓋的面積應是影響其光合作用效率的重要因素。伏石蕨及柳葉劍蕨的可孕性葉可以乘載孢子並有著和非孕性葉相似的光合作用效率，這可能是因為可孕性葉可能透過結構上的改變（如改變氣孔排列）使葉片能有如此功能但壽命較短可能為其代價。本研究針對兩種蕨類的二型性推論，伏石蕨及柳葉劍蕨的可孕性葉可能有著提高其繁殖量的優勢但付出壽命較短的代價。此主題還有許多值得繼續探討的面向，如景天酸代謝、葉片復水性等抗旱特徵和二型性的關聯等，需要更多研究才能較完整地了解蕨類「非孕性葉－可孕性葉」二型性的生理與生態意涵。

The source and energy of plants are limited such that there are often trade-offs among growth, survival, reproduction and photosynthesis. Ferns primarily reproduce through spores, and the production of spores may affect key physiological processes such as photosynthesis. However, studies on this topic is limited to date. Some ferns have dimorphic leaves, one type produces spores, known as fertile leaves, and another type does not, known as sterile leaves. Previous studies on ferns with dimorphic leaves have mostly focused on terrestrial species, where the fertile leaves are almost completely filled with spores, resulting in reduced photosynthetic efficiency relative to sterile leaves. However, because ferns exhibit a wide variety of leaf and growth forms, previous studies have covered only a small portion of fern species, and therefore, the generalizability of their findings remains uncertain. This study examines two epiphytic ferns Lemmaphyllum microphyllum and Lomariopsis flaccida with dimorphic leaves, exploring differences in phenology, physiological ecology, and morphological characteristics between the two types of leaves, such as photosynthetic efficiency, stomatal density, osmotic potential, and chlorophyll concentration. The goal is to explain how these dimorphic ferns balance reproduction and photosynthesis, and the strategies they employ to adapt to these processes. The results showed no significant differences in photosynthetic efficiency, osmotic potential, or chlorophyll concentration between fertile and sterile leaves in both species. However, stomatal density of the fertile leaves was significantly higher than that of the infertile leaves. Additionally, for Lomariopsis flaccida, stomatal conductance and intracellular CO₂ concentration were not significantly different between the two types of leaves. This study, suggests that leaf area and the portion of the leaf covered by sporangia (spore-producing structures) could be important factors influencing the photosynthetic efficiency of fertile leaves. Both Lemmaphyllum microphyllum and Lomariopsis flaccida have fertile leaves capable of bearing spores while maintaining photosynthetic efficiency similar to that of infertile leaves. This suggests that structural modifications, such as changes in stomatal arrangement, may enable the fertile leaves to maintain much of the photosynthetic function, but this may come at the cost of a shorter lifespan. It is proposed that the fertile leaves of L. microphyllum and L. flaccida may provide an advantage by enhancing reproductive output at the cost of life span. There are still many hypotheses and research directions yet to be explored, such as the relationship between dimorphism and drought resistance traits like crassulacean acid metabolism (CAM) and leaf rehydration. Much work remains to be done in order to deepen our understanding of the ecophysiology of"sterile leaf - fertile leaf" dimorphism in ferns.