苔蘚著生大型真菌之養分利用形式與對宿主的影響

Abstract

已知真菌除了腐生，也能和維管束植物建立互利共生、片利共生或寄生關係，兩者 的交互作用對生態系的結構及運作有重要的影響，然而真菌與苔蘚 (非維管束植物) 間 的交互關係則較少被研究。雖然有些大型真菌的子實體經常出現在苔蘚周圍或上面，但 對於這些真菌與苔蘚間的交互關係所知甚少。本論文探討苔蘚著生真菌 (bryophyte- associated fungi) 的養分利用模式，以了解這些真菌是否會與苔蘚建立共生關係 (包含 寄生、片利共生至互利共生)。論文的第一部份我探討中研院院區內兩種著生在走燈苔 (Plagiomnium acutum) 上的真菌 Galerina cf. minima 與 Rickenella fibula 是否有從活的苔 類宿主獲取養分，並檢視這兩種苔生真菌在走燈苔宿主植株內的分佈區域、對宿主的生 理表現和宿主植株內真菌相的影響。論文的第二部份則探討生長在太平山森林遊樂區及 鴛鴦湖自然保留區的苔蘚著生真菌，分析這些採集樣本以及其他已知養分利用模式的真 菌與植物之碳、氮穩定同位素比值 (𝛅13C 和𝛅15N)，以推測野外苔蘚著生真菌的養分利 用模式。結果經由組織切片與定序，確認走燈苔植株內有 G. cf. minima 與 R. fibula 生 長，其菌絲主要分佈在假莖中心;穩定同位素分析顯示 G. cf. minima 與 R. fibula 可能從 活的走燈苔獲得碳，並與宿主交換氮;葉綠素螢光測量結果則發現兩真菌著生對走燈苔 的光合作用潛能有中性或正面的影響;次世代定序結果顯示走燈苔在被 G. cf. minima 或 R. fibula 著生時，其植株內的真菌相組成顯著不同。推測 G. cf. minima 和 R. fibula 為走 燈苔的弱寄生內生真菌。太平山及鴛鴦湖採集到的苔蘚著生真菌經由分子鑑定後發現至 少有 9 屬，其中主要為粉褶菌屬 (Entoloma) 與盔孢傘屬 (Galerina)，Entoloma spp.又依 據其𝛅13C 和𝛅15N 可分成兩群。其中 E. cf. indigoferum、E. cf. brevispermum、E. cf. murrayi 及 E. cf. quadratum 的𝛅13C 和𝛅15N 值與已知外生菌根菌相近，表示它們可能從活宿主上 獲取碳，並提供氮;另一群包含 E. cf. conferendum 及 E. cf. strictius，其𝛅13C 和𝛅15N 則 是和腐生真菌較相似;Galerina spp.的𝛅13C 及𝛅15N 值與維管束植物相近，表示它們可能 單方面從活宿主獲取養分。因此太平山及鴛鴦湖保留區的苔蘚著生 Entoloma spp.至少有兩種獲得養分的途徑，有些與苔蘚間可能有養分交流的現象，其餘則較接近腐生菌;苔蘚著生 Galerina spp.可能為苔蘚寄生菌。本研究結果顯示苔蘚著生真菌與苔蘚有共生關 係，兩者之交互作用形式可能比原先想像的更多樣。

Fungi not only decompose organic matter to obtain nutrients, but also establish mutualistic, commensal, or parasitic relationships with vascular plants, exerting significant impacts on ecosystem functioning. However, little is known about the interactions between fungi and bryophytes. Certain macrofungi are observed producing fruiting bodies in close proximity to bryophytes, known as bryophyte-associated fungi; however, the nature of their relationships with bryophytes remains ambiguous. In this study, I aim to elucidate the trophic modes of bryophyte-associated fungi and to understand whether these fungi can establish symbiotic relationships with bryophytes. The first part of my thesis focused on the fungi Galerina cf. minima and Rickenella fibula, which I observed fruiting on the moss Plagiomnium acutum, to understand whether these two moss-associated fungi can acquire nutrient from the living moss host. To further explore the interactions between these two fungi and the moss, I also investigated the location of these fungi in moss tissues, measured the photosynthetic potential of P. acutum, and analyzed the mycobiome composition of P. acutum. Results of isotopic analyses indicated that both G. cf. minima and R. fibula obtained carbohydrates from the living moss and might exchange nitrogen with the host. Histological section and DNA sequencing results showed that both G. cf. minima and R. fibula grew inside P. acutum, primarily in the center of stem tissues. These two fungi appeared to have neutral to positive effect on the photosynthetic potential of the moss. Based on the amplicon sequencing results, the presence of R. fibula or G. cf. minima had significant impact on mycobiome assemblies of the moss rhizoids. The results suggest that G. cf. minima and R. fibula are weak parasitic endophytes obtaining carbon from the host P. acutum. In the second part, more bryophyte-associated fungi in Taipingshan and Yuanyang Lake were examined to reveal their possible trophic modes. I analyzed the natural abundance of carbon (𝛅13C) and nitrogen (𝛅15N) stable isotopes in these fungi, and subsequently compared the results with fungal species with known trophic modes, as well as plants, to infer their nutrient sources. I found that Entoloma and Galerina made up the majority bryophyte-associated fungi in the field survey. According to 𝛅13C and 𝛅15N, Entoloma spp. can be divided into two groups. The 𝛅13C and 𝛅15N of E. cf. indigoferum, E. cf. brevispermum, E. cf. murrayi and E. cf. quadratum were similar to those of known ectomycorrhizal fungi, implying that they obtained carbon from a living host and transferred nitrogen in return. The 𝛅13C and 𝛅15N of E. cf. conferendum and E. cf. strictius were more similar to those of known saprotrophic fungi. Both 𝛅13C and 𝛅15N values of Galerina spp. were close to those of plants, suggesting that they unilaterally acquired nutrient from living hosts. Thus, the bryophyte-associated Entoloma spp. exhibit at least two distinct trophic modes. Some of these Entoloma spp. may engage in nutrient exchange with bryophytes, while others appear to be saprotrophs. The bryophyte-associated Galerina spp. may be parasitic fungi of bryophyte. This study highlights the presence of the symbiotic relationships between bryophyte-associated fungi and bryophytes, revealing a greater diversity in these relationships than previously anticipated.