Factors influencing survival of vesicular-arbuscular mycorrhiza propagules during topsoil storage.
The survival dynamics of VAM fungi were determined by bioassay for soils stored for 0.5-6 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 with the breaking point occurring at -2 MPa. The addition of length of storage time contributed significantly to the accuracy of the model. The data suggested 2 separate populations of VAM fungi: those propagules in soils with moisture potentials < -2 MPa and those in soils at > -2 MPa. Soil moisture and length of storage time had differing effects on each of these populations. When water potential was < -2 MPa moisture was an important predictor of inoculum, while length of storage had little predictive capability. However, when water potentials were > -2 MPa the predictive importance of soil moisture and length of storage was reversed. The results are discussed in relation to topsoil replacement and subsequent plant community development.