Stable isotope signatures of underground seedlings reveal the organic matter gained by adult orchids from mycorrhizal fungi

1.Orchids produce dust seeds dependent on the provision of organic carbon by mycorrhizal fungi for their early development stages. Hence, all chlorophyllous orchids experience a dramatic switch in trophic strategies from initial mycoheterotrophy to either autotrophy or partial mycoheterotrophy during ontogeny. Yet, the degree to which partially mycoheterotrophic orchids gain carbon from their mycorrhizal fungi is unclear based on existing approaches.

2.Here, we propose a novel approach to quantify the fungal-derived organic matter gain of chlorophyllous mature orchids mycorrhizal with rhizoctonia fungi using the stable isotope signatures of their fully mycoheterotrophic (FMH) seedlings in a linear two-source mixing model.

3.We conducted a field germination experiment with seven orchid species and measured carbon, nitrogen and hydrogen stable isotope natural abundances and nitrogen concentrations of mature orchids, underground seedlings and autotrophic references.

4.After in sit...