The presence of mycorrhizas, proteoid roots and leguminous nodules was determined in a range of
woodland species (from a variety of habitats in soils formed on different parent materials) in the Kakadu
area in the monsoonal tropics of northern Australia. In addition, the chemical fertility and the occurrence
of mycorrhizal fungi and rhizobia in rudimentary soils ('minesoils') forming in situ on waste rock dumps
at a mine site in the region were compared with stockpiled topsoils from the mine area and undisturbed
topsoils collected from the surrounding native woodland. A major aim of these investigations was
to assess the feasibility of rehabilitating the waste rock dumps without spreading topsoils.
More than 90% of the woodland flora examined had one or more specialised nutrient-gathering
mechanism. Mycorrhizas were found on 82% of the species, with some 16% of species having both
ecto and VA mycorrhizas, often on the same individual plant. Many of these observations are the
first records of mycorrhizal infection in the particular genera and species involved. Soil baiting and
dilution experiments showed that rhizobia and mycorrhizal fungi were ubiquitous components of the
soil biota in all undisturbed woodland soils. However, they were absent or poorly represented in the
stockpiled topsoils and in some of the rudimentary soils formed in waste rock at the mine site. The
diversity of spore types and/or numbers of infective propagules of VAM fungi was lower in stockpiled
topsoils and in minesoils than in the undisturbed woodland soils. Nutrient omission experiments identified
that acute deficiency of P, and to a lesser extent N, was a limitation to growth of seedlings on all
soils. Zn deficiency was detected in the only soil for which this was examined. A glasshouse experiment,
using a young minesoil and application of basal nutrients, demonstrated that inoculation of Acacia
holosericea seedlings with rhizobium could completely alleviate the effects of N deficiency. Under
conditions of both N and P deficiency, dual inoculation of A. holosericea with rhizobium and spores
of the VAM fungus, Glomus, only partly overcame the limitations of P deficiency on seedling growth.
Induction of deficiencies of P and Zn in a second minesoil (through application of basal nutrients),
demonstrated that inoculation of seedlings of Eucalyptus pellita with spores of the ectomycorrhizal
fungus, Scleroderma, partly alleviated the effects of both deficiencies.
Rehabilitation strategies implemented at the mine site using either soils forming in situ on the waste
rock dumps, or by spreading stockpiled topsoils, will need to ensure deficiencies of P and other nutrients
are alleviated and that viable populations of mycorrhizal fungi and rhizobia are introduced and maintained
during early phases of vegetation establishment.
Physical dispersion of radioactive mine waste at the rehabilitated Radium Hill uranium mine site,South Australia
