Goodyera repens Br. was either grown from seed and infected with its natural mycorrhizal endophyte, Ceratobasidium cornigerum (Bourd.) Rogers, or obtained as natural mycorrhizal plants from the field. Insoluble [14C]carbohydrate was provided at a point source available only to the external mycorrhizal mycelium of protocorms, plantlets (up to 50 mg w wt) or plants. Protocorms and plantlets obtained 14C via their external mycelium but plants did not, even when stressed for carbon by being kept in darkness for two weeks. There was no enhancement of growth of mycorrhizal plants when a carbon source was present in the substrate over an eight-week period. When 14CO2 was fed to plant shoots to monitor movement of carbon from plant to endophyte, there was no evidence of such movement over a 7 d period.
These results suggest that carbon moves only from fungus to orchid and that this movement ceases when the host reaches a certain stage of development. With respect to carbon, mature green plants of G. repens appear to be independent of their mycorrhizal association.