Title: Orchid diversity hotspots: a bunch of fussy plants or easy-going neighbours? Exploring mycorrhizal fungal diversity across sympatric forest orchids in New Zealand
Applicant: Dr Carlos Lehnebach and Dr Lara Shepherd
Recent studies have shown that coexisting orchid species have distinct mycorrhizal associates. Since specialisation to specific fungal symbionts can reduce competition between sympatric species it has been suggested that these differences may have important ecological implications and influence orchids’ local abundance and distribution. However, a contrasting scenario, where plants from mixed-species populations exhibit low specificity for fungal symbionts, has also been reported. Here competition among species is avoided by having a rather opportunistic approach to fungal partnerships. Whether similar patterns of mycorrhizal associations can explain local orchid hotspots in New Zealand is unknown.
This project will characterise the mycorrhizal fungal community found in roots of co-occurring species of orchids growing under southern beech forest in the North Island of New Zealand. By using next-generation sequencing technologies we will generate a thorough representation of each orchid’s fungal associates. We expect that this approach will allow us to identify uncommon and unculturable fungal entities commonly undetected by other methods. Many of the orchid genera we will study here include threatened or uncommon species so we expect that our findings will serve as baseline information to assist in their conservation and infer potential causes driving their rarity. At a larger scale, this study will contribute to understanding the evolution of mycorrhizal association in orchids that have dispersed over long distances and colonised island environments such as New Zealand.
Our study aims to:
1) Characterise the diversity of fungal associates in co-occurring species of epiphytic and terrestrial orchids
2) Determine whether orchid hotspot consists of species with distinct/similar mycorrhizal associations
3) Determine whether mycorrhizal preferences of sympatric orchids vary across orchid habit (epiphytic v/s terrestrial) and trophic strategy (photosynthetic v/s myco-heterotrophic).
Our research included 16 species of epiphytic and terrestrial orchids growing in the lower part of the North Island of New Zealand. These represent 11 orchid genera; Acianthus, Caladenia, Chiloglottis, Corybas, Cyrtostylis, Drymoanthus, Earina, Gastrodia, Microtis, Pterostylis and Thelymitra. The main fungal families associated with these orchids belong to the families Ceratobasidiaceae, Mycenaceae, Physalacriaceae, Russulaceae, Sebacinaceae, Serendepitaceae and Tullasnelaceae.
Overall, our results showed different scenarios for the orchid-mycorrhizal interaction. For instance, our data suggest that different species of orchids growing side by side form partnerships with fungi from different families, possibly to avoid competition. However, this does not apply to all the species we studied, and widespread and common orchids such as Thelymitra longifolia and Pterostylis alobula, associate mostly with fungus of the same family (i.e. Ceratobasidiaceae). Second, not all orchid species are loyal to their fungal partners, and Gastrodia cunnighamii for instance, associates with fungus from three different families at three different sites; Sebacinaceae (Sebacina sp.), Physalacriaceae (Armillaria sp.) and Mycenaceae (Mycena sp.). While in other orchids, such as Caladenia chlorostyla, the same fungal family (Serendepitaceae) was retrieved from plants growing at different sites. Third, we noticed the diversity of the fungal community within the orchid root fluctuates over time and the reproductive state of the plant.
This research has considerably advanced our knowledge of mycorrhizal interactions and specificity in New Zealand orchids. Both the results and the experienced gained during this project will support our future studies into the propagation (symbiotic seed germination) and in situ and ex situ conservation of New Zealand’s most threatened orchids.
Research articles and conference presentations arising from this project
Lehnebach CA & Shepherd LD. 2020. Unearthing hidden alliances and unfaithful partners – exploring the diversity of mycorrhizal interactions across a selected group of New Zealand orchids. New Zealand Native Orchid Journal 157: 20–25. (open access in 2021)
Lehnebach CA, Shepherd L. 2019. Exploring mycorrhizal fungal diversity across sympatric forest orchids in New Zealand. ASBS-NZPCN Conference. Wellington, New Zealand. (See pages 57–58 for abstract, URL https://systematics.ourplants.org/wp-content/uploads/2019/11/Taxonomy-for-Plant-Conservation-2019-Proceedings.pdf)
Lehnebach CA. 2018. Orchid research news. New Zealand Native Orchid Group Journal 147: 19. http://www.nativeorchids.co.nz/Journals/PDF/NZNOJ_147.pdf
Lehnebach CA, Shepherd LD, van der Walt K, Alderton-Moss J. 2019. Exploring orchid-mycorrhizal interactions in New Zealand to understand hot-spots and guide conservation actions. VII International Orchid Conservation Congress, Kew Gardens. London, UK. (Link to conference abstracts http://www.zandonaconservacao.com.br/gallery/iocc%20booklet.pdf)