Field inoculation with arbuscular mycorrhizal fungi in rehabilitation of mine sites with native vegetation, including Acacia spp.

Field experiments were conducted at rehabilitation sites at two contrasting mines in Western Australia. At both mines, Acacia spp. are important components of the rehabilitation ecosystem. At a mineral sands mine near Eneabba, dry-root inoculum of the arbuscular mycorrhizal (AM) fungus Glomus invermaium (WUM 10) was introduced into riplines with three rates of phosphate fertiliser application. Plants were assessed for mycorrhizal colonisation and phosphorus status. There was no plant growth benefit from inoculation. A considerable number of infective propagules of indigenous AM fungi was already present in the topsoil. The inoculant fungus as well as the indigenous AM fungi formed mycorrhizas, but only in a small number of Acacia and other native plant species. In a study of AM fungal inoculation at a gold mine rehabilitation site at Boddington, dry-root inoculum of G. invermaium was applied to riplines prior to seeding. Despite apparently ideal environmental conditions, colonisation of native seedlings was limited. Possible reasons for this were investigated in further experiments that addressed environmental factors such as soil temperature and moisture and factors such as the age of the plant and presence of a colonised cover crop. Inoculum remained infective even under moist conditions in field soil for at least 4 months. Its infectivity decreased in parallel with falling temperatures. However, the level of infectivity present did not ensure extensive colonisation of native plants such as Acacia seedlings in the field. Susceptibility of Acacia seedlings to colonisation by AM fungi appeared to be seasonal, as colonisation increased with increasing daytime temperatures and daylight hours.