BayCEER Workshop 2016

Which fungi taste good to orchids? Diversity of carbon and nitrogen gaining strategies in mycoheterotrophic orchids of Southeast Asia

Introduction

Orchids start their lives as mycoheterotrophic (MH) plants relying on carbon (C) and nutrient supply from mycorrhizal fungi. Later in their development, most orchids produce green leaves and rely on autotrophy. However there are some orchids which still rely on their fungal partners to some extent, ranging from partially MH (chlorophyllous) to fully MH (achlorophyllous) orchids. A center of biodiversity of MH orchids is found in Southeast Asia. Little is known about their fungal partners and despite the large number of fully MH orchids no reports about partially MH orchids exist.

Material and Methods

We used stable istope abundances of C and nitrogen (N) and applied a two-source mixing model to compare the C and N source of orchids from Taiwan and China relative to autotrophic non-orchid reference plants from the same microhabitat. We sampled the chlorophyllous genus Neottia (represented by 5 species) and the achlorophyllous fully MH genera Lecanorchis (3 species) and Epipogium (1 species). Each orchid was collected along with 2 – 4 reference plants within a 1m² plot in 3 – 5 replications. We normalized the data to compare different sites by calculating enrichment factors for every plot. We are using molecular techniques to identify the fungal partners from roots samples of orchids.

Results

Whereas most Neottia species show the same isotope signatures as autotrophic reference plants, some green Neottia species were enriched in ¹⁵N, probably gaining N from fungi although no fungal C gain was detected. The MH orchids showed strong but different enrichment in both ¹³C and ¹⁵N within genera and even within species, indictating association with different functional fungal groups (ectomycorrhizal vs. saptroptrophic fungi).

Conclusions

This study does not provide direct evidence for partial mycoheterotrophy in Neottia sp., however we cannot yet rule this out. Fungal associations within fully MH orchids may be more complex than so far assumed.