Beneficial soil microorganisms of the Jarrah forest and their recovery in bauxite Southwestern Australia

Beneficial soil microorganisms are integral to nutrient availability and uptake for plants in restoration. They include mycorrhizal fungi and nitrogen-fixing bacteria, together with the soil microbial populations which contribute to nutrient availability. Around 70% of jarrah forest plant species form arbuscular mycorrhizas, and approximately a quarter also form ectomycorrttizas. Many are also legumes. In addition, around 70 orchid species depend on mycorrhizal symbioses. Therefore, symbiotic soil microorganisms are important in the ecosystem. Arbuscular mycorrhizal fungi recover to pre-mining levels in bauxite restoration in five years. Ectomycorrhizal fungi are poorly adapted to disturbance; however, they are able to reinvade through wind-blown spores. The density of ectomycorrhizal fungi has been found to be equivalent in seven-year-old restoration and adjacent forest, but both abundance and diversity are correlated with development of a litter layer. Fortunately, rhizobia are known to be tolerant of soil disturbance, and failure of N-fixation by legumes has not been reported in restoration. Other N-fixing symbioses, such as between Allocasuarina and Frankia or Macrozamia and Nostoc, have not been investigated in restored mines. Soil microbial biomass C achieves near equivalence after about eight years and appears to be driven by vegetation productivity and related inputs of C into the soil. There is little field evidence that the absence, or very low levels, of soil microbial symbionts will have a substantial impact on plant growth in restoration. Therefore, deliberate reintroduction of these microorganisms does not appear justified. However, soil management to enhance the survival of soil biological components is recommended.