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.
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