Stable isotope signatures and specific mycobionts reveal the mycoheterotrophic nutrient acquisition of Danxiaorchis yangii.

Fully mycoheterotrophic orchids rely entirely on fungal symbionts for carbon acquisition, are often highly specialized in their fungal associations, and exhibit stable isotope signatures distinct from autotrophic plants. Danxiaorchis yangii is a rare, leafless orchid endemic to subtropical China whose nutritional ecology has not been previously examined. We combined high-throughput fungal community profiling with multi-element stable isotope natural abundance analyses (δ¹³C, δ¹⁵N, δ²H, δ¹⁸O) to investigate fungal associations and nutrient acquisition in D. yangii. Mycorrhizal rhizomes were dominated by a single operational taxonomic unit affiliated with the wood-decaying saprotroph Candolleomyces candolleanus (Psathyrellaceae), with additional low-abundance taxa related to Ramariopsis (Clavariaceae). Stable isotope signatures showed strong enrichment in ¹³C, ¹⁵N, and ²H relative to co-occurring autotrophic plants, confirming a fully mycoheterotrophic nutritional mode. Notably, the magnitude of nitrogen isotope enrichment differed from that reported for other Psathyrellaceae-associated orchids, suggesting greater complexity in nitrogen acquisition within saprotroph-based mycoheterotrophic systems.