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) habi tats in a seasonally-dry tropical region in the Northern Territory of Austr alia into open-pot cultures was undertaken to supplement knowledge about th e diversity of those fungi. This experiment considered factors affecting th e diversity of fungi obtained in trap cultures started using diluted soil f rom field sites and two host plants. A range of soil phosphorus and other n utrient levels from severely deficient to sufficient for maximal growth was used to determine the impact of nutrition on mycorrhizal associations of s orghum (Sorghum sp.) and clover (Trifolium subterraneum). Soil cores taken from pots at 6-week intervals provided roots and soil to assess mycorrhiza formation and sporulation without substantial damage to plants. The identif ication of VAM fungi to genus by observing morphological patterns within cl over roots revealed substantial differences in fungus populations between s oils and a moderate effect of nutrient levels on fungal diversity. Changes in the proportion of different fungi in roots over the 31 weeks of the expe riment were also observed. Glomus spp. were initially the most abundant fun gi within roots, but Scutellospora spp. gradually became more dominant at l ater harvests, while colonisation by Acaulospora spp. was limited at all ti mes. For both clover and sorghum, sporulation was limited and was dominated by single species of Scutellospora and Acaulospora. This contrasted with t he much higher diversity of spore types in the original field soils.