|Liebel, HT; Gebauer, G: Stable isotope signatures confirm carbon and nitrogen gain through ectomycorrhizas in the ghost orchid Epipogium aphyllum Swartz, Plant Biology, 13, 270-275 (2011), doi:10.1111/j.1438-8677.2010.00369.x|
Epipogium aphyllum is a rare Eurasian achlorophyllous forest orchid known to associate with fungi forming ectomycorrhizas, while closely related orchids from warm and humid climate depend on wood- or litter-decomposer fungi. We conducted 13C and 15N stable isotope natural abundance analyses to identify the organic nutrient source of E. aphyllum collected in Central Norway. Stable isotope data of orchid shoot tissues in comparison to accompanying autotrophic plants document a carbon and nitrogen flow from ectomycorrhizal fungi to the orchid. DNA data obtained from fungal pelotons in the orchid root cortex confirm the presence of Inocybe and Hebeloma, both fungi known to form ectomycorrhizas. The enrichment factors for 13C and 15N of E. aphyllum are used to calculate a new overall average enrichment factor for mycoheterotrophic plants living in association with ectomycorrhizal fungi (ε 13C ± 1 SD of 7.2 ± 1.6 ‰ and ε 15N ± 1 SD of 12.8 ± 3.9 ‰). These values can be used to estimate the fungal contribution to the organic nutrient uptake by partially mycoheterotrophic plants where fully mycoheterotrophic plants are lacking. N concentrations in the orchid tissue were found to be unusually high and significantly higher than in accompanying autotrophic plant leaf samples. This may be caused by nitrogen gain of E. aphyllum from obligate ectomycorrhizal fungi. In summary, we show that E. aphyllum is an epiparasitic mycoheterotrophic orchid depending on ectomycorrhizal Inocybe and Hebeloma fungi to obtain carbon and nitrogen through a tripartite system linking mycoheterotrophic plants through fungi with forest trees.
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