Ectomycorrhizas in Eucalyptus tetrodonta and E. miniata Forest Communities in Tropical Northern Australia and their Role in the Rehabilitation of these Forests Following Mining

Abstract

The importance of ectomycorrhizas in Eucalyptus tetrodonta F.Muell. and E. miniata Cunn. ex Schauer dominated forests and woodland communities in the monsoonal tropics of northern Australia was assessed. Ectomycorrhizas colonised between 24 and 54% of final order lateral roots in soil cores collected at 16 native forest sites. Only a minority of the plant species present formed ectomycorrhizas (mainly eucalypts and acacias) but these species contributed more than 75% of the basal area. More than 70 species of putative ectomycorrhizal fungi were collected, with three hypogeous taxa (Nothocastoreum, Hysterangium and an undescribed Boletaceae) most frequently encountered. Glasshouse inoculation experiments confirmed that a diverse range of fungi was capable of forming ectomycorrhizas with E. tetrodonta and E. miniata seedlings, and that the growth of both species could be substantially increased by inoculation with specific fungi. The fungi most effective in increasing seedling growth were generally those which most extensively colonised the seedling roots. A second component of this study investigated the requirements for ectomycorrhizal fungi in native forest rehabilitation following mining. Ectomycorrhizal infectivity was low in disturbed soils and mine spoil materials, with the intensity of disturbance and the presence of regrowth vegetation key determinants of the level of infectivity. Inoculation of seedlings of E. miniata with spores of ectomycorrhizal fungi increased both growth and leaf phosphorus concentrations by between two- and three-fold at 7 months after planting out on a waste rock dump devoid of native ectomycorrhizal propagules. The application of these findings to minesite rehabilitation in the region, and the feasibility of using spores for broad-scale inoculation, are discussed.