The Loss of Va Mycorrhizal Infectivity During Bauxite Mining May Limit the Growth of Acacia pulchella R.Br.

We used plant bioassays to monitor the decline in infectivity of VA mycorrhizal fungi in topsoil during bauxite mining. In a second experiment, we investigated the seasonal changes in the infectivity of VA mycorrhizal fungi in jarrah (Eucalyptus marginata Donn ex Smith) forest soil. Finally, we tested the hypothesis that Acacia pulchella growing in soil disturbed during bauxite mining would respond to phosphorus and to inoculation with VA mycorrhizal fungi. During bauxite mining in the Western Australian jarrah forest, the infectivity of propagules of VA mycorrhizal fungi in topsoil was destroyed, even when the soil was stripped and respread promptly without stockpiling. Most infectivity was lost within 3 weeks of clearing the vegetation, before the soil was disturbed. The rapid loss of infectivity may be associated with the absence of spores in the soil. In a revegetated, respread soil, the infectivity of VA rnycorrhizal fungi was substantially greater than that of freshly disturbed soil, but less than levels recorded in similar undisturbed forest soil. There were no clear seasonal changes in VA mycorrhizal infectivity, indicating that the loss of infectivity during mining was not a seasonal response. Dry matter production by Acacia pulchella, in a glasshouse experiment, was at least doubled if soil from experiment 1 was inoculated with effective VA mycorrhizal fungi.