臺灣白及的原地萌芽與原球莖內真菌多樣性之探討

Abstract

蘭科是植物最大的科之一，具有極高的物種多樣性，然而近年卻逐漸受到環境變遷、棲地干擾與過度採集的威脅。其中，白及屬為臺灣原生蘭中少數同時具藥用與觀賞價值的蘭科植物。相較其它蘭科植物的胚發育，臺灣白及，具有較多的胚細胞數與分化、種子可於水中萌發，以及相對廣泛的分佈等特性，因此本研究欲探討此物種於原生地的萌發限制因子，以及原球莖是否必須與真菌共生。本研究於臺灣全島六處臺灣白及原生地進行種子原地萌發試驗，將超過三千個種子袋埋設於各樣區，分別埋藏於植株旁與遠離植株處，每三個月回收部分種子袋，計算萌發率與種子活性。使用illumina MiSeq分析萌發原球莖中的真菌菌相，以墨水染色確定真菌是否定殖，並以穩定同位素分析確認萌發的原球莖是否仰賴真菌提供營養。結果顯示，臺灣白及種子於其原生地可於一個月內萌發，且於特定樣區萌發率可達近60%。埋藏於臺灣白及植株附近與遠離植株的種子袋的萌發率並無顯著差異，且距離植株的距離與方位亦不影響萌發率，顯示離植株之遠近非影響種子萌發之關鍵因素。然而，萌發率在不同樣區間具有顯著差異，且各樣區的萌發率與樣區溫度變化、降雨量與相對濕度變化具有相關性。真菌菌相分析結果顯示白及原球莖內存在Oxyporus、Fusarium、Serendipita等多種真菌，顯示此物種萌發時仍與絲核菌共生。不同樣區間真菌多樣性差異不大，真菌菌相組成則有顯著差異。原球莖墨水染色顯示60 %的原球莖有真菌定殖，每個原球莖內僅有1.2%的細胞含有菌絲團。穩定碳氮同位素分析則進一步確認了臺灣白及在原球莖階段仍會與真菌共生以獲得碳源。綜上所述，臺灣白及的種子於原生地萌發快速且萌發率高，然其萌發率與樣區環境變動相關，且共生真菌在原生境的萌發過程中仍扮演重要的角色。

Orchidaceae, one of the most diverse plant families, is increasingly threatened by environmental changes, habitat disturbance and overcollection. Among them, Bletilla species are valued for both ornamental use and medicinal properties. Bletilla formosana, a terrestrial orchid native to Taiwan, is particularly interesting due to its advanced embryo, ability to germinate in sterile substrates, and broad distribution. This study aims to explore the factors that constrain its germination in nature and determine if fungal association is necessary. In situ germination experiments were conducted at six sites in Taiwan, where over three thousand seed packets were buried in areas with and without conspecific plant. Germination and seed viability were assessed at 1, 3, 6, and 9 months after burying, and fungal communities in germinated protocorms were analyzed using Illumina MiSeq sequencing. Ink staining and stable isotopes were used to explore fungal colonization and trophic mode during germination. Our results showed that seeds could germinate within a month, with median germination reaching 58% at one site. Germination did not differ between occupied and unoccupied areas, nor was it influenced by distance or direction from conspecific plants, suggesting that proximity to adult orchids is not a key factor. However, germination varied significantly across sites and was moderately correlated with fluctuations in temperature, precipitation and relative humidity. The predominant fungi associated with germinated protocorms included Oxyporus, Fusarium and Serendipita, revealing that this species still associates with Rhizoctonia-like fungi during germination. Ink staining of protocorms revealed fungal colonization in 60% of protocorms, with only 1.2% of cells per protocorm containing pelotons. Stable isotope analysis confirmed that B. formosana remains dependent on fungi for carbon acquisition during germination. In summary, B. formosana exhibits rapid and high germination success in nature. Its germination is correlated with environmental fluctuations across sites, and protocorms remain dependent on fungi for carbon acquisition.