Acacias respond to additions of phosphorus and to inoculation with VA mycorrhizal fungi in soils stockpiled during mineral sand mining

Three pot experiments were conducted to test the hypothesis that the growth of Acacia spp. in stockpiled soil from two mineral sand mines, could be increased by the addition of phosphorus (P) or inoculation with VA mycorrhizal fungi. In soils from North Stradbroke Island, the dry weight of shoots of Acacia concurrens was increased by P and by VA mycorrhizal fungi in tailings sand, while in less adsorptive topsoil dry weight was only increased at low levels of applied P. When A. concurrens was grown in a layer of topsoil placed over tailings sand, shoot dry weight increased, in response to inoculation with VA mycorrhizal fungi banded between the soil layers. In topsoil from Eneabba, the dry weight of shoots at low rates of applied P was increased by up to 4 times by inoculation with VA mycorrhizal fungi. The response to inoculation in both experiments was due to increases in the uptake of P by the plants. Species of VA mycorrhizal fungi differed in their ability to increase plant growth. However, in soils from both sites, the same fungal species were effective.