The secret to conserving an endangered orchid is in the soil

A study of orchids shows the secret to conservation isn't in the plants you can see, but the fungi you can't.

The metallic sun orchid Thelymitra epipactoides is endangered in its home in Australia. Now presumed extinct in New South Wales, it survives in Western Victoria and the south-east corner of South Australia. It grows in heathland near the coast, but rising temperatures mean that some locations might not be viable in the future. A team from Royal Botanic Gardens Victoria, the Australian National University and RMIT University have been examining some endangered orchids to see what gives them the best chance of success. They started with something familiar to orchid hobbyists around the world, mycorrhizal fungi.

Thelymitra epipactoides
Thelymitra epipactoides, the Metallic Sun Orchid. Photo: Dr Noushka Reiter.

Lead author of the study Dr Noushka Reiter, who manages RBG Victoria’s Orchid Conservation Program, explained: “Mycorrhizal fungi are incredibly important to plants, and the majority of plants have mycorrhizal associations. These super industrious fungi help in all sorts of ways, by providing nutrients to plants and in some cases added protection from disease. Orchids, in particular, are completely dependent on their mycorrhizal partners, requiring their presence to germinate in the wild.”

Dr Reiter said: “Our study is on an orchid found in eastern Australia in temperate areas, one of the main concerns for orchids in these areas with changing climate is not only an increase in temperature but changes in rainfall, with some areas predicted to become drier under climate change a kind of double whammy for some species in temperate areas.

mycorrhizal fungi
The mycorrhizal fungi studied. Photo: Dr Noushka Reiter.

“We found there are two species of fungi associated with this orchid, one found in the drier warmer site and the other found in the wetter, cooler sites. The two species had different optimal germination temperatures for the orchid, the fungi found in the drier warmer site germinated seed at the cooler temperatures (typical of autumn-winter temperature) and the fungi found in the wetter cooler site germinated fungi in warmer temperatures.”

Orchids have specialised into a staggering number of species. There are more species in this one family of plants than all species of birds and mammals put together. It means that there can be quite specific requirements when it comes to conservation. Dr Reiter said: “Orchids are specialised in many ways, in some cases through highly specific fungal associations in others with specialised pollinator associations, each orchid has its own story to tell with mycorrhizal associations. Pollinators and habitat associations need to be understood to conserve and to conduct successful conservation translocations.”

You might assume that one way to translocate a species would be to look for an environment with the same plants as the orchid’s home habitat. However, Dr Reiter and her colleagues found it wasn’t so simple as matching plants. She said: “This is the first study to look at co-planting in such a way, certainly suggesting that it is beneficial to take associated vegetation in to account, as some species as this study shows are likely to cause a reduction in growth of the orchid compared to others.”

The paper marks a significant study in orchid conservation: “This is particularly important for orchid conservation as far as re-introductions / conservation translocations are concerned as it shows with some species they may utilise different mycorrhiza in different habitats and thus the fungi may need to be matched to the habitat of the re-introduction site.”

It seems future plant conservators will need to be keenly interested in fungi too, and willing to be ruthless with some other plants in the habitats that they plant in.

Reference List

Reiter, N., Lawrie, A. C., & Linde, C. C. (2018). Matching symbiotic associations of an endangered orchid to habitat to improve conservation outcomes. Annals of Botany. https://doi.org/10.1093/aob/mcy094