臺灣殼斗科森林之真菌菌相探討

Abstract

真菌在自然環境中扮演著多樣且重要的角色，其豐富性可直接反映生態系統的穩定性和功能性，故對於永續生態管理，了解森林真菌群是至關重要的。本研究中，我們以八種殼斗科物種作為研究材料，採集樹葉、枝條、落葉及土壤等四種介質，共864個樣本的真菌ITS2區域進行擴增，再以高通量分子條碼(metabarcoding) 技術，調查臺灣熱帶及亞熱帶森林的真菌多樣性及組成。採集點之海拔落於500至2500公尺之間。分析結果共鑑定了11,600個擴增子序列變異(Amplicon sequencing variants; ASVs)，平均每樣本有69個，於其中有兩個普遍存在且無顯著生態為偏好的ASV，分類上分別屬於Cladosporium sp.及Pyrenochaetopsis sp.。由樹葉、枝條及落葉組成的葉際中，共享的ASV有12個，平均佔樣本相對豐度的5%。在α多樣性分析上，落葉的真菌多樣性最高，其次為葉子及枝條，而土壤在這四種介質中則最低。在真菌的組成上，受地理位置影響最為顯著，其次為介質、季節及寄主物種。高海拔的樣本(超過1500 公尺)在真菌組成上較低海拔樣本(低於800公尺)更為相似。分析結果顯示，同物種寄主的真菌組成在不同森林中存在差異，其相似度會隨著海拔高度的增加而升高。季節變化對真菌整體多樣性有顯著影響，其中長期的降雨量為主導因素。在組成比例上，子囊菌門的真菌佔比最高，又以一Cladosporium sp.最為優勢。這佔有高豐度的Cladosporium ASV也是本研究分析結果中唯一的關鍵物種，且後續藉由長片段擴增子定序技術(Long amplicon sequencing)驗證為單一物種。我們的研究深入了解了臺灣闊葉林的真菌多樣性，揭示了海拔驅動的變化、季節影響，以及關鍵物種— Clasoporium sp.的優勢。

Diversity of the fungal community directly reflects the stability of the whole ecological system. Understanding the forest mycobiome is crucial for managing ecosystems sustainably. In this study, we investigated the fungal diversity of seven Fagaceae species in tropical and subtropical forests in Taiwan using a metabarcoding approach by sequencing ITS3/ITS4 amplicon in a total of 864 samples across four different substrates (leaf, twig, litter and soil). The locations of the trees range in altitude from 500 to 2500 meters. We identified a total of 11,600 amplicon sequencing variants (ASVs) with averaging 69 ASVs per sample. There were two ubiquitous ASVs, Cladosporium and Pyrenochaetopsis, with unclassified species and no significant niche preference. Phyllosphere, including leaf, twig, and litter, shared 12 ASVs, accounting on average 5% of samples’ relative abundance. Across substrates, higher α-diversity was observed in litter than twig and leaf, while soil had the lowest diversity. Mycobiome composition was most significantly influenced by host tree’s location, followed by substrates, season, and host species. Samples from high altitudes (over 1500 m) had a similar composition compared to those from low altitudes (below 800 m). Our results revealed that the mycobiome composition varies across forests from same host species, and had a tendency of being similar along with the altitude. Seasonal changes have a significant influence on the total fungal diversity, with long-term precipitation serves as the predominant factor. The majority of the observed mycobiome was composed of Ascomycota taxa, with a Cladosporium sp. as the dominant ASV. The prevalent Cladosporium ASV is also detected as the only keystone species in our study and is verified as a single species via long amplicon sequencing of the full ribosomal operon. Our study brings insight into the fungal diversity of Taiwanese broadleaf forests, revealing altitude-driven variations, seasonal influences, and the dominance of the keystone species — Cladosporium sp.