Investigations on mycorrhizal associates and nutritional resources of mycoheterotrophic orchids in Taiwan
Final Report Abstract
About 1% of all orchid species are achlorophyllous throughout their entire life cycle and depend on their mycorrhizal partners for carbon and mineral nutrient supply. These orchids are known as full mycoheterotrophs. With more than 120 species as compared to just two species in entire Europe, tropical and subtropical Asia is a hotspot of fully mycoheterotrophic orchids. Fungi forming simultaneously ectomycorrhizas with forest trees have been identified as hosts of mycoheterotrophic orchids in temperate regions. In contrast, the few data available for mycoheterotrophic orchids from tropical and subtropical regions provide evidence for a much wider diversity of fungal hosts. In this German-Taiwanese partner project we investigated the fungal hosts using molecular methods and the type of nutrient source using multielement stable isotope abundance analysis of 12 out of the about 50 fully mycoheterotrophic orchid species from five genera growing in different forest types and elevation zones in Taiwan. A wide range of fungal hosts spanning from ectomycorrhizal fungi to litter- and wooddecay fungi with species- and genera-specific, but also location-dependent preferences was found. Carbon and nitrogen stable isotope abundance patterns confirmed tissues of litter- or wood-decay or ectomycorrhizal fungi as nutrient sources of the investigated orchid species, while hydrogen isotope abundance supported the general heterotrophic mode of nutrition. Furthermore, we investigated along developmental stages (protocorm, seedling, adult) changes in the nutrition of the chlorophyllous orchid Cremastra appendiculata. This species is unique concerning its mycorrhizal partners switching from non-rhizoctonia saprotrophic Psathyrellaceae in early stage rhizomes to rhizoctonia fungi in the roots of adults. Isotope signatures suggest autotrophic nutrition of mature C. appendiculata, while isotope signatures of protocorms indicated fully mycoheterotrophic nutrition. Seedlings showed an intermediate isotope signature. Unfortunately, the COVID-19 pandemic hampered our time schedule seriously. Gaps in the original work schedule arising from these delays were filled with three additional mycoheterotrophy-related subprojects: (1) We investigated the fungal partners and nutritional mode of Neuwiedia malipoensis, a representative of the earliest diverging orchid lineage, Apostasioideae. Our data indicate a transition in mycorrhizal partners exclusively belonging to the rhizoctonias during ontogenetic development with decreasing dependency of N. malipoensis on fungal carbon and nitrogen. This finding contrasts N. malipoensis from the ectomycorrhizal-associated Apostasia nipponica and indicates different resource acquisition strategies already within this earliest diverging orchid lineage. (2) We investigated for the first time stable isotope signatures of fungal pelotons extracted from orchid roots associated with ectomycorrhizal or rhizoctonia fungi and compared these data to the respective orchid and reference plant tissues. With this approach we provided the first isotope signatures of rhizoctonia fungi. (3) Using a multi-element stable isotope approach, we provided first evidence for the occurrence of partial mycoheterotrophy among arbuscular mycorrhizal tree seedlings under the heavily light-limited conditions in the understory of tropical forests.
Publications
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Fungal association and root morphology shift stepwise during ontogenesis of orchidCremastra appendiculatatowards autotrophic nutrition. AoB PLANTS, 14(3).
Zahn, Franziska E.; Lee, Yung-I. & Gebauer, Gerhard
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Novel insights into orchid mycorrhiza functioning from stable isotope signatures of fungal pelotons. New Phytologist, 239(4), 1449-1463.
Zahn, Franziska E.; Söll, Erik; Chapin, Thomas K.; Wang, Deyi; Gomes, Sofia I. F.; Hynson, Nicole A.; Pausch, Johanna & Gebauer, Gerhard
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Mode of carbon gain and fungal associations of Neuwiedia malipoensis within the evolutionarily early-diverging orchid subfamily Apostasioideae. Annals of Botany, 134(3), 511-520.
Zahn, Franziska E.; Jiang, Hong; Lee, Yung-I. & Gebauer, Gerhard
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Stable isotope analysis indicates partial mycoheterotrophy in arbuscular mycorrhizal woody seedlings in tropical forests [Dataset]. Dryad.
Zahn F.E., Contreras B., Engelbrecht B.M.J. & Gebauer G.
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Stable isotope analysis indicates partial mycoheterotrophy in arbuscular mycorrhizal woody seedlings in tropical forests. Functional Ecology, 38(12), 2720-2733.
Zahn, Franziska E.; Contreras, Blexein; Engelbrecht, Bettina M. J. & Gebauer, Gerhard
