Vesicular-arbuscular mycorrhizae in taconite tailings. I. Incidence and spread of endogonaceous fungi following reclamation

The incidence and spread of vesicular-arbuscular (VA) mycorrhizae in reclaimed and unreclaimed taconite tailings were assessed. A corn bioassay was used to determined the relative levels of infective propagules of VA mycorrhizal fungi in tailing samples collected before and periodically after reclamation of a 144-ha taconite tailing settling basin in Wisconsin, U.S.A. Samples were collected at three distances from the western berm of the settling basin to attempt to monitor the spatial establishment and spread of mycorrhizae in the basin. There was a significant temporal effect, but no distinguishable spatial effect on the population densities of VA mycorrhizal propagules in the tailing samples. The relative levels of mycorrhizal propagules in samples collected before reclamation were not significantly different from the levels in sterilized controls. Tailings collected 1, 8 and 20 weeks after reclamation had progressively higher densities of infective propagules. These results contrast with the very slow rates of spread reported for studies conducted in semi-arid sites in North America. It was suggested that VA mycorrhizal fungi are able to become established more rapidly in mesic sites than semi-arid sites because mesic sites are generally more conducive to host plant growth.