FUNCTIONAL COMPATIBILITY IN ARBUSCULAR MYCORRHIZAS MEASURED AS HYPHALP TRANSPORT TO THE PLANT

The functional compatibility of symbioses between host plants and arbu scular 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, BEG15) and Glomus inverm aium Hall (isolate WUM10) or left uninoculated and grown for 28 days i n soil divided into three compartments. One side compartment was separ ated from the main compartment by a 20 mu m nylon mesh, and radioactiv e labelling with P-32 was used to determine hyphal P uptake. The other side compartment was separated from the main compartment by a 700 mu m nylon mesh and P-33 was used to determine the combined P uptake by r oots and hyphae. All plant-fungus combinations were compatible with re spect to mycorrhiza formation, measured both as root colonization and growth of external hyphae. In contrast, the symbioses differed markedl y with respect to functional compatibility as phosphorus uptake by eac h fungus depended on the species of host plant. The hyphal transport o f P-32 was high in G. caledonium in symbioses with all three plant spe cies, whereas G. invermaium transported significant amounts of P-32 on ly when associated with flax. Consequently, to determine the P-transpo rt effectiveness of a mycorrhizal fungus is meaningful only in the con text of its associated host plant species.