SUMMARYThe infectivity of vesicular-arbuscular (VA) mycorrhizal fungi m three soils from different vegetation types was compared before and after disturbance. The relative quantities of infective propagules in the disturbed soils were estimated by an infectivity test after the soils were diluted. Spore numbers and mycorrhizal roots were also quantified in each soil.The mycorrhizal colonization of clover roots in tbe infectivity test was not decreased after soil from an annual pasture had been disturbed. In contrast, in both a forest soil and a heathland soil, the percentage root length colonized of test plants was almost halved if the soils had been disturbed. In the pasture soil up to 10 times or 25 times more propagules survived disturbance than in the forest soil or the beatbland soil respectively. The large number of propagules may allow the VA mycorrbizal fungi in the pasture soil to maintain maximum infectivity after soil disturbance.

SUMMARYWe condLicted Iwo nhisshousc experiments to determine the cH'ect of soil disturhiiiu'c on tlie inlcctiNity of external hyphae of vesieuU\r-;irhuscular (V.^) mycorrhizal fungi. A nylon mesh was used to exclude plant roots while allowing fungal h\phae lo grow into soil contained hy the mesh. Hyphae of \.\ mycorrhizal fungi that had heen separated from the original host plant root were still ahle to colonize bioassay plants rapidly and cxtensi\ely. However, disturhance of the soil inside the mesh, hy mixing for ! min, almost eliminated subsequent \".\ mycorrhiza formation in that soil. Damage to the soil hyphal network by soil disturbance may contribute to the losses in mycorrhizal infectivity that have been observed after mining and cultivation.

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SUM M.Ain'We examined the hypothesis that hyphae of a V.A mycorrhizal fungus in dry soil remain infecti\ e, hut that the infectivity decreases if the soil is disturbed. We used split-pots, and sealed cylinders of nylon mesh, to create \()lunic's of dry soil which contained hyphae of Acaulospora lacvis Gerd. and Trappe that were attached, outside the mesh, to roots of li\ iiiK jilanls of .Acacia saligna. (Lahill.) H. Wentll. After the soil was dried //; situ, the hyphae were detaclied from tlie roots without soil disturhance, or the soil containing the hyphae was disturhed. The infectivity of the hyphae after these treatments was then compared with tliat of intact hyphae.External h>phae of A. laevis remained highh-infectixe in soil in which the inatric potential had reached -21 MI'a. Myphae detached from the original host plant roots were equally infectixe. However, distiu-hance of the dry soil containing the external hyphae severely reduced the infectivity of the hyphae. .After tluorescent staining, fungal structures with fluorescing nuclei were readily \isihle lioth within, and attached to, roots of A. saligna which had no fluorescing nuclei.

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 ectomycorrhizas. 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.