Glomalean mycorrhizal fungi from tropical Australia. II, The effect of nutrient levels and host species on the isolation of fungi

The isolation of vesicular-arbuscular mycorrhizal(VAM) fungi from natural (savanna, rocky hill,wetland and rainforest) and disturbed (minesite) habitatsin a seasonally-dry tropical region in the Northern Territory of Australia into open-pot cultures was undertakento supplement knowledge about the diversityof these fungi. This experiment considered factors affectingthe diversity of fungi obtained in trap culturesstarted using diluted soil from field sites and two hostplants. A range of soil phosphorus and other nutrientlevels from severely deficient to sufficient for maximalgrowth was used to determine the impact of nutritionon mycorrhizal associations of sorghum (Sorghum sp.)and clover (Trifolium subterraneum). Soil cores takenfrom pots at 6-week intervals provided roots and soil toassess mycorrhiza formation and sporulation withoutsubstantial damage to plants. The identification ofVAM fungi to genus by observing morphological patternswithin clover roots revealed substantial differencesin fungus populations between soils and a moderateeffect of nutrient levels on fungal diversity. Changesin the proportion of different fungi in roots over the 31weeks of the experiment were also observed. Glomusspp. were initially the most abundant fungi withinroots, but Scutellospora spp. gradually became moredominant at later harvests, while colonisation by Acaulosporaspp. was limited at all times. For both cloverand sorghum, sporulation was limited and was dominatedby single species of Scutellospora and Acaulospora.This contrasted with the much higher diversity ofspore types in the original field soils.