Factors Influencing Survival of Vesicular-Arbuscular Mycorrhiza Propagules During Topsoil Storage

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Abstract
The survival dynamics of vesicular-arbuscular mycorrhizal (VAM) fungi were determined, (using a bioassay procedure) for soils stored from 0.5-6.0 yr in topsoil stockpiles associated with a coal surface-mine in the western USA. Propagule mortality could best be related to in situ soil moisture potential using a piecewise regression model (R2 = 0.57; P .ltoreq. 0.001) with the breaking point occurring at -2 MPa. The addition of length of storage time contributed significantly to the accuracy of the model (R2 = 0.70; P .ltoreq. 0.001). In addition, the piece-wise nature of the data suggested 2 separate populations of VAM fungi-those propagules found in soils with moisture potentials less than -2 MPA [pascal] and those occurring in soils with moisture potentials greater than -2 MPa. Soil moisture and length of storage time had differing effects on each of these populations. When water potential was less than -2 MPa, moisture was an important predictor of inoculum (P < 0.001), while length of storage had little predictive capability (P = 0.17). However, when water potentials were greater than -2 MPa, the predictive importance of soil moisture (P = 0.86) and length of storage (P = 0.04) were reversed. The significance of these findings to topsoil replacement and subsequent plant community development are discussed.