Investigations on mycorrhizal associates and nutritional resources of mycoheterotrophic orchids in Taiwan

大约1%的兰花是无叶绿素植物，在整个生命周期中依赖菌根伙伴提供碳和矿物质营养。这些无叶绿素的兰花被称为真菌异养植物。在温带和北方森林，真菌异养兰花与外生菌根真菌的狭窄分支相关联，并通过地下菌根网络从邻近树木获得光合产物。与这些发现相反，据报道，在热带和亚热带森林中，有几种真菌异养兰花与腐养性非根核真菌有关，并通过其木材或凋落物腐烂的能力获得营养。尽管如此，也有报道在亚热带森林中发现了与外生菌根相关的分枝异养兰花。因此，在亚热带和热带森林中，与木材或凋落物腐烂真菌和外生菌根真菌相关的真菌异养兰花可能共存。与温带地区（例如整个欧洲只有两种异养真菌兰花）相比，亚洲热带和亚热带地区的异养真菌兰花种类繁多（超过120种）。台湾原生兰花约400种，其中16属50余种。台湾大多数异养真菌兰花的真菌伴侣和营养模式尚不清楚。在该项目中，我们将使用分子方法、多元素稳定同位素自然丰度方法和示踪剂应用对6个属的广泛的真菌异养兰物种进行研究，并实现以下目标：(1)我们将鉴定20多个真菌异养兰物种的真菌联系物。(2)利用宏基因组分析方法比较这些兰花菌根真菌多样性（OTUs）。(3)为了揭示其营养资源，对不同森林类型和山地高坡带不同真菌类群的异养真菌兰科植物的碳、氮、氢、氧稳定同位素自然丰度进行了分析，并与共生的完全自养植物进行了比较。本研究可望取得以下成果：(1)鉴定目标兰花的菌根伴生物，了解台湾原生异养型兰花的菌根多样性、特异性及分布模式。(2)在不同的高/低海拔生境和不同的森林类型中，我们将追踪与不同菌根伴侣相关的目标兰花物种的营养资源和养分流动。

About 1 % of all orchid species is achlorophyllous and depends on mycorrhizal partners for carbon and mineral nutrient supplies throughout their entire life cycle. These achlorophyllous orchids are known as mycoheterotrophic plants. In temperate and boreal forests, mycoheterotrophic orchids associate with narrow clades of ectomycorrhizal fungi and obtain photosynthates from neighbouring trees through underground mycorrhizal networks. In contrast to these findings, in tropical and subtropical forests a couple of mycoheterotrophic orchids have been reported to associate with saprotrophic non-rhizoctonia fungi and obtain nutrients through their ability of wood- or litter-decay. Nonetheless, also ectomycorrhizal-associated mycoheterotrophic orchids have been reported for subtropical forests. Thus, for subtropical and tropical forests a co-occurrence of mycoheterotrophic orchids associated with wood or litter-decay fungi and with ectomycorrhizal fungi is likely. As compared to the temperate region (e.g. two mycoheterotrophic orchid species in entire Europe), a great diversity of mycoheterotrophic orchids (more than 120 species) occurs in tropical and subtropical Asia. In Taiwan, among the ca. 400 native orchids, more than 50 fully MH orchids of 16 genera were recorded. The fungal partners and nutritional modes of most mycoheterotrophic orchids in Taiwan are still unknown. In this joint call project of MOST-DFG we will use molecular methods together with a multi-element stable isotope natural abundance approach and tracer applications to investigate a wide range of mycoheterotrophic orchid species from six genera and to address the following objectives:(1) We are going to identify the fungal associates of more than 20 mycoheterotrophic orchid species.(2) We are going to compare the fungal diversity (OTUs) in mycorrhiza of these orchids using metagenomic analysis.(3) To reveal their nutritional resources, we are going to analyze carbon, nitrogen, hydrogen and oxygen stable isotope natural abundances of mycoheterotrophic orchids associated with different fungal groups in various forest types and mountain elevation zones and compare these isotope abundances to co-occurring fully autotrophic plants.From this project we expect to obtain the following results:(1) We will identify the mycorrhizal associates of the target orchid species studied in this project and understand the mycorrhizal diversity, specificity and distribution patterns of native mycoheterotrophic orchids in Taiwan.(2) We will trace the nutritional resources and nutrient flows of the target orchid species associated with different mycorrhizal partners and occurring in various habitats from high/low elevation and different forest types.