Understanding orchid adaptability to climate change
Orchids are one of the largest families of flowering plants, with around 30 000 species worldwide. They disperse very small seeds that can be caught in air currents and transported over large distances, though the vast majority of seeds fall very close to the parent plant. “While other seed types tend to contain nutrient reserves to support plants until they can produce their own food, orchid seeds are more like dust – the embryo contains just 50 to 100 cells surrounded by a seed coat,” explains FORECAST(opens in new window) project coordinator Mike Fay from the Royal Botanic Gardens, Kew(opens in new window) in the United Kingdom. “There is also this bizarre relationship with fungi. The only way orchids can germinate is by being infected by a fungus.” In most orchids, fungi are restricted to the roots and underground parts. Some species have even done away with photosynthesis and live off fungi their entire life.
‘Canary in the coal mine’ for ecosystem change
The FORECAST project, which was supported by the Marie Skłodowska-Curie Actions(opens in new window) programme, sought to examine this relationship between orchids and fungi and assess the potential impact of climate change in areas with Mediterranean climates. “Orchids cannot survive without fungi,” says Fay. “If the orchid adapts to climate change in a different way than the fungus, the orchid could be in big trouble.” This very specific relationship orchids have with fungi – as well as with pollinators – means that they are the ‘canary in the coal mine’ for ecosystem change. If orchids begin to disappear, then something is going wrong.
Recording temperature and humidity levels of soil
In FORECAST, project fellow Jacopo Calevo, also from the Royal Botanic Gardens, Kew, set out to analyse the impact of climate change by examining species from Western Australia and Mediterranean Europe. “Australian orchids in particular are exposed to extreme temperatures,” he explains. “Soil temperatures range from zero in winter, to nearly 70 degrees in the summer, as soil heats up.” Many Australian species adapt to these extreme temperatures by burying tubers deep in the soil where temperatures are more stable. Calevo built computational models to predict how these orchids might survive if temperatures were to shift a little, and carried out field experiments to record temperature and humidity levels of soil. “What we found was that even in the most extreme climate scenarios, orchids will likely survive,” he adds. “This is because they have experienced temperature extremes and been able to adapt. In fact, while orchid seeds were shown to be able to survive extreme temperatures, fungal mycelium was found to be more sensitive.”
Raising awareness of the complex nature of orchids
A key conclusion is that while orchids themselves have been shown to be adaptable, the impact of climate change – and indeed habitat destruction – could influence the presence of fungi in the soil. This could have profound consequences for many orchid species. “Around 60 % of orchid species are threatened, which is higher than for other flowering plants,” notes Fay, “in part because of this special relationship orchids have with fungus and pollinators. We already know that climate change has caused the local extinction of certain species.” Another lesson to be drawn is that orchids need to be conserved where they are, as each species fills a particular niche in the local ecosystem. Both Fay and Calevo hope that FORECAST will raise awareness of the delicate and complex nature of orchids and improve conservation efforts.
