Scientists have discovered that orchids depend on fungi living in decaying wood to sprout and survive their earliest stages. This hidden partnership reveals a new carbon pathway linking deadwood to living plants.
Fungi that decompose deadwood provide a vital food source for orchids when they begin to grow, supplying carbon that their extremely small seeds lack. Researchers at Kobe University found that this relationship fills a long-standing gap in knowledge about how wild orchids survive their earliest stage and also highlights an overlooked flow of carbon through forest ecosystems.
Orchid seeds are about the size of dust particles and contain no nutrients to support early growth. While mature orchids are known to depend on specific fungi that form structures inside their roots, scientists had not confirmed whether those fungi also play a role during germination. “Studying orchid germination in nature is notoriously difficult. In particular, the painstaking methods required for recovering their seedlings from soil explain why most earlier studies focused only on adult roots, where fungi are easier to sample,” explains Kobe University plant evolutionary ecologist Kenji Suetsugu.
While conducting fieldwork, Suetsugu and his colleagues began to notice an unusual pattern. “We repeatedly found seedlings and adults with juvenile root structures near decaying logs, not scattered randomly in the forest. That recurring pattern inspired us to test whether deadwood fungi fuel orchid beginnings,” he says.
These juvenile root structures, known as coral-shaped rhizomes, are thought to be seedling organs that persist into adulthood — and they are commonly linked to fungi that decompose wood rather than the fungi typically found in adult orchids that lack these structures. With their background in orchid ecology and evolution, the team set out to determine which fungi support young orchids.
Writing in the journal Functional Ecology, the Kobe University researchers report that when they buried seeds from four model orchid species at different sites in the forest, germination occurred only near decaying logs. The resulting seedlings were almost entirely associated with wood-decomposing fungi.
“We were struck by how exclusive and consistent these fungal partnerships were. There is an almost perfect match in the fungi that seedlings of a given orchid species associate with and the fungi on adult plants with coral-shaped rhizomes of the same species. We think that the plants without coral-shaped rhizomes shift to other fungi as their nutritional needs change during growth and the carbon source offered by rotting logs dries out,” says Suetsugu.
Reference: “The nexus of decay and birth: Ecological and evolutionary significance of wood-decaying fungi in green Calypsoinae orchid germination” by Kenji Suetsugu and Hidehito Okada, 30 September 2025, Functional Ecology.
DOI: 10.1111/1365-2435.70181
This research was funded by the Japan Science and Technology Agency (grants JPMJPR21D6, JPMJFR2339), the Japan Society for the Promotion of Science (grant JP25H00944) and the Research Institute for Humanity and Nature.
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