The functional compatibility of symbioses between host plants and arbuscular mycorrhizal fungi was measured as hyphal P transport to plants. Cucumber (Cucumis sativus L.), wheat (Triticum aestivum L.) and flax (Linum usitatissimum L.) were inoculated with Glomus caledonium (Nicol. & Gerd.) Trappe & Gerdemann (isolate RIS42, BEG 15) and Glomus invermaium Hall (isolate WUM10) or left uninoculated and grown for 28 days in soil divided into three compartments. One side compartment was separated from the main compartment by a 20 um nylon mesh, and radioactive labelling with 32P was used to determine hyphal P uptake. The other side compartment was separated from the main compartment by a 700 um nylon mesh and 33P was used to determine the combined P‘uptake by roots and hyphae.
All plant-fungus combinations were compatible with respect to mycorrhiza formation, measured both as root colonization and growth of external hyphae. In contrast, the symbioses differed markedly with respect to functional compatibility as phosphorus uptake by each fungus depended on the species of host plant. The hyphal transport of 32P was high in G. caledonium in symbioses with all three plant species, whereas G. invermaium transported significant amounts of 32P only when associated with flax. Consequently, to determine the P-transport effectiveness of a mycorrhizal fungus is meaningful only in the context of its associated host plant species.