Didymoplexis Orchids: The Hidden World of Fungal Partnerships

Orchids in the Didymoplexis genus are fascinating. They belong to a large group of plants that rely solely on fungi for their food. These orchids are part of the Gastrodieae tribe, which is one of the biggest groups of fully mycoheterotrophic orchids. Mycoheterotrophic means they get their nutrients from fungi. These plants are found in subtropical and tropical forests across Taiwan. Didymoplexis orchids have a unique way of getting their nutrients. They form partnerships with different types of fungi. Some of these fungi break down dead plant material, while others help trees absorb water and nutrients from the soil. These fungi are called saprotrophic fungi and ectomycorrhizal fungi. Didymoplexis orchids have a preference for saprotrophic fungi. However, Didymoplexis siamensis has a different approach. It mainly partners with ectomycorrhizal fungi, particularly those from the Sebacinales group. But it also teams up with wood-decaying fungi called Delicatula. Scientists used special techniques to study these partnerships. They found that Didymoplexis pallens and Didymoplexis micradenia mostly associate with fungi that break down leaf litter. These fungi include Mycena, Clitocybula, Marasmius, and Gymnopus. There were also some ectomycorrhizal and rhizoctonia fungi involved, but they played a smaller role. Didymoplexis siamensis, on the other hand, had a different mix. It primarily partnered with ectomycorrhizal fungi, but also had a significant relationship with wood-decaying Delicatula. This mix of fungal partners helps Didymoplexis siamensis get the carbon and nitrogen it needs. The way these orchids get their nutrients is quite interesting. Scientists looked at the carbon and nitrogen isotopes in the orchids. They found that the patterns matched what is known for fully mycoheterotrophic orchids that partner with litter or wood-decaying fungi. The nitrogen isotope levels in Didymoplexis species were different from those in orchids that only partner with ectomycorrhizal fungi. Even though Didymoplexis siamensis partners with ectomycorrhizal fungi, it had lower nitrogen isotope levels and higher carbon isotope levels than expected. This suggests that the wood-decaying Delicatula fungi play a big role in meeting its nutritional needs. The findings about Didymoplexis orchids and their fungal partners are important. They help us understand how these plants survive and thrive in their environments. This knowledge can also help in conserving these unique orchids and the ecosystems they inhabit. It is important to note that this is still a developing field of research.