Patterns of initial saprophytic fungal colonization of grass roots from two severely disturbed soils

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Abstract
Development of the root-surface fungal assemblages of Agropyron trachycaulum grown on amended oil-sands tailings and a subalpine coal-mine spoil from Alberta (Canada) was followed over one growing season. Fungi were isolated, using a root-washing procedure, from the region of main seminal and nodal roots 4 cm from the root–hypocotyl axis. Fungal colonization of the root surfaces was rapid, with equilibrium numbers of species reached 2 weeks after plant emergence. Although the application of either fertilizer, peat, or sewage sludge to these spoils had no effect on the general form of the colonization curve, peat amendation did result in significantly higher numbers of species on the root surfaces. Species turnover within all assemblages was high throughout the growing season. The amount of species replacement ranged from a low of 67% to a high of 91% between consecutive 4-week sampling periods. Thus, although the number of species was relatively constant, species composition changed considerably. The structure of the root-surface fungal assemblages was characterized by a large proportion of rare species. The species abundance distributions were essentially negative exponential. Neither time nor amendation had any significant effect on these distributions. The large incidence of rare species within the assemblages suggests that these root surfaces represent nonequilibrium systems with respect to species occurrences.