ICOM1 Abstract

session 1 Dickson, Sandy1, Sally Smith1 & andrew Smith2. 1Department of Soil Science, Waite Campus, University of Adelaide, S. Australia 5064, 2Department of Botany, University of Adelaide, S. Australia 5005. - P fluxes from two VA mycorrhizal fungi to leeks under two soil phosphate levels An experiment was carried out to demonstrate the efficiency of transfer of P by two VA mycorrhizal fungi. Two soil P levels were used (no added P (P0) and 0.4 mmol P per kg soil (P1)), with two fungi (Glomus sp. ‘City Beach’ WUM 16 and Scutellospora calospora) on the host plant Allium porrum. Harvests were taken at 2,3,4 and 6 weeks and fungal efficiency was measured as the flux (transfer of P to the plant per unit area of symbiotic interface). Vital staining to show metabolically active fungal structures was carried out on sections, in order to quantify intercellular hyphae, arbuscules and vesicles within the root. The percent of root colonised was also measured using non-vital staining of root segments. Although the results using the two stains were not significantly different, there was a trend for sections with vital staining to show slightly lower levels of (viable) colonisation than those stained with a non-vital stain. Flux values have been obtained using the percent colonisation shown by vital staining as the measure of active arbuscules and hyphae. Fluxes across both the intercellular and arbuscular interfaces, or across the arbuscular interface alone, vary with the fungal species and with the addition of P in the soil. At P0 fluxes were low with both fungi (0.81 - 6.57 nmol m2 s-1 ). In contrast, fluxes across both interfaces were greatly increased at P1, but to differing degrees depending on the fungus. It appears that S. calospora is more tolerant of additional P in the soil than is Glomus sp. ‘City Beach’.