MYCORRHIZAS IN THE KAKADU REGION OF TROPICAL AUSTRALIA .1. PROPAGULESOF MYCORRHIZAL FUNGI AND SOIL PROPERTIES IN NATURAL HABITATS

This research represents the first part of a study which aimed to char acterize the role of mycorrhizal associations in undisturbed and distu rbed habitats in the Alligator Rivers Region of the Northern Territory of Australia. This is a seasonally dry tropical region with a climate consisting of a long dry season and a monsoonal wet season. Intact so il cores were sampled from 22 sites in this region, representing eucal ypt savanna woodland, wetland, rocky hill and rainforest habitats. Clo ver, sorghum and eucalypt seedlings were grown in these cores in bioas says to measure the inoculum potential of vesicular-arbuscular mycorrh izal (VAM) and ectomycorrhizal (ECM) fungi. Propagules of VAM fungi we re concentrated in the surface horizon, and were not adversely affecte d by 6 months dry storage of soil. Bioassays detected VAM fungus propa gules at all sites, but these were less numerous in three sites with s parse herbaceous vegetation (a shrub-dominated woodland site, a sandst one area and a disturbed gravel pit without topsoil), than in other wo odland sites. Propagules of VAM fungi were particularly numerous in so il from a rainforest habitat, which had much denser plant cover than a ny of the savanna sites. Propagules of ECM fungi colonized eucalypt se edling roots in some cores from all sites, except two wetland areas an d a disturbed area without eucalypt trees. Physical and chemical prope rties of soils varied between sites and some properties (texture, orga nic carbon, etc.) were correlated with the inoculum potential of VAM f ungi.