Investigating the role of mycorrhizal communities in the conservation and restoration of Drymoanthus adversus and D. flavus, two epiphytic orchids endemic to New Zealand.

Mainland New Zealand (NZ) and its offshore islands are home to more than 100 species of orchids, 70% of these are endemic and 35% threatened. Most of NZ’s orchids are terrestrial, with only nine species growing as epiphytes on trees and shrubs. The genus Drymoanthus, which is also found in Australia and New Caledonia, is represented in NZ by D. adversus (Fig. 1) and D. flavus (Fig. 2). D. adversus is considered common and widespread while D. flavus is uncommon and classified as At Risk – Declining. Both species are however threatened by illegal collection and droughts. The conservation and restoration of orchids needs to ascertain that the requirements for seed germination and establishment, including orchid mycorrhizal fungi (OMF), are met.

Figure 1. D. adversus in situ

The project team has successfully grown both Drymoanthus species in vitro using asymbiotic methods and established protocols to transfer these seedlings to nursery conditions (Fig. 3) for both Drymoanthus species. In addition, pilot studies revealed that within the same study site, Drymoanthus adversus and D. flavus associate with different OMF species from Ceratobasidiaceae and Tulasnellaceae. Interestingly, in vitro symbiotic germination trials found only Ceratobasidiaceae supported seed germination and seedling development for both D. adversus and D. flavus. However, sample sizes were limited to a small number of individuals from each species (5-10) growing on the same host tree and thus are unlikely to reflect the mycorrhizal diversity within and between populations.

Figure 2. D.-flavus-in-habitat

This project therefore aims to expand on the pilot studies and improve the conservation and management of D. adversus and D. flavus in NZ. Variation in OMF between host trees is a key aspect for the dispersal and long-term survival of orchid populations. Using culture-dependent and culture-independent methods, we will investigate the OMF that associate with D. adversus and D. flavus over three years and compare OMF between host and non-host tree species. Our study will furthermore use herbarium specimens dating back to 1769 to investigate if the OMF associations of Drymoanthus have changed through time and correlate any changes with climatic data. We anticipate that the results will enable us to identify micro-environments required by Drymoanthus for seed germination and reintroduction of in vitro generated seedlings. These outcomes will also benefit the conservation of epiphytic orchids in the Pacific and beyond.

Figure 3. transferred-D.-adversus-seedlings-scaled