BayCEER Workshop 2020

Partial mycoheterotrophy is a nutrition mode of green, terrestrial orchids in Taiwan

Orchids exhibit different nutritional strategies and associate with diverse fungi, however, little is known about nutrition modes of (sub-)tropical orchids. Our study aimed at the distribution of partial mycoheterotrophy among a selection of chlorophyllous, terrestrial orchid species in Taiwan. Partial mycoheterotrophy is an intermediate trophical tactic whereby plants gain carbon from both, photosynthesis and associating fungi. Multi-element natural stable isotope analyses (¹³C, ¹⁵N, ²H, ¹⁸O) of seven green orchid species, the fully mycoheterotrophic Eulophia zollingeri and autotrophic reference plants from different sites in Taiwan as well as molecular analyses were examined to identify trophical strategies and fungal partners. Mycoheterotrophic protocorms of chlorophyllous Cremastra appendiculata were additionally analysed to investigate a possible change in fungal community during transition from initial mycoheterotrophy to the adult´s nutrition mode. E. zollingeri and C. appendiculata protocorms showed isotopic signature characteristic for orchid specimens entirely relying on fungal carbon and were associated with saprotrophic non-rhizoctonia Psathyrellaceae. Investigated mature green orchids probably associate with rhizoctonia fungi. Fungal community of C. appendiculata changed from non-rhizoctonia saprotrophic Coprinellus species in its early development stage to Tulasnellaceae rhizoctonial fungi in the mature phase concomitant with a shift from initial mycoheterotrophy to autotrophy. Relative enrichment in ²H revealed ‘cryptic’ partial mycoheterotrophy among Eulophia graminea, E. dentata, E. pelorica and Oreorchis indica providing first evidence that partial mycoheterotrophy occurs among the Oreorchis genus and could be widespread among the large Eulophia genus. We demonstrate that partial mycoheterotrophy among green, terrestrial orchids appears at various habitats and elevations in (sub-)tropical Taiwan and is thus not limited to temperate regions.