Mycorrhizal specificity of fully mycoheterotrophic <i>Yoania</i> in Taiwan and China and novel natural abundance stable isotope patterns

Yoania is a rare achlorophyllous mycoheterotrophic orchid genus distributed across Japan, Taiwan, China, India and Vietnam, associating with wood-decomposing fungi. Studying mycoheterotrophic plants' mycorrhizal diversity is essential, as they depend entirely on fungi for carbon and nutrients. Here, we studied mycorrhizal interactions and nutrient strategies in three Yoania species from Taiwan and China. We hypothesize (H1) that Physisporinus associates with the Yoania species studied, and (H2) that when this symbiotic relationship alters nutritional patterns, this partnership will result in lower δ¹³C enrichment than in other fully mycoheterotrophic, wood-decaying-fungus-associated orchids. High-throughput DNA sequencing was used to investigate the mycorrhizal fungal communities of three Yoania species. In addition, natural stable isotopes (δ¹³C and δ¹⁵N) were measured in two species, while δ²H and δ¹⁸O were measured in one of them to further evaluate nutrient acquisition strategies. In Taiwan, Yoania japonica and Yoania amagiensis var. squamipes, and in China, Yoania prainii, all associate with a single Physisporinus taxonomic unit, distinct from the Physisporinus taxonomic units associated with Yoania species in Japan. As a white-rot fungus, Physisporinus may preferentially decompose relatively ¹³C depleted lignin likely explaining the lower ¹³C enrichment of Yoania in comparison with other fully mycoheterotrophic orchids associated with wood-decomposing fungi. Our combined molecular and isotopic evidence suggests that the mycoheterotrophic orchid genus Yoania employs a nutritional strategy that is most likely linked to the use of lignin by its white-root fungal partner in forest ecosystems.