Taxonomy and Ecology Of Inland Sand Dune ... - Mycorrhizae

54spores in the soil (Moorman and Reeves,1979). My MIP data reflect Weaver'searly (1926) observation that fibrousroot systems such as those found in O.hymenoides decrease with increasingsoil depth. Data from cultivated soil(Sutton and Barron, 1972; Smith, 1978),from grassland soil (Sparling andTinker, 1975), and from semi-arid soil(Schwab and Reeves, 1981) also supportour results. These observations stronglysupport Redhead's (1977) conclusionthat VAM decrease markedly below 15cm and are consistent with similarobservations of Warcup (1951) forsaprobic fungi. Mycorrhizae and fungalpropagules of VAM may occur at muchgreater depths in soil than those depthsthat we examined. Zajicek et al. (1986)found both colonization percent andcolonization intensity decreased withincreasing depth in Tallgrass or Trueprairie species, but Glomus fasciculatum(Thaxter) Gerdemann & Trappe emend.Walker & Koske was associated withforb roots at depths to 220 cm.However, they neither measured theMIP of the soil nor determined theviability of spores.Laboratory and greenhouse studies onthe relationship between water potentialand germination of vesicular arbuscularmycorrhizal spores (Koske, 1981b;Tommerup, 1983; and Wilson, 1984)indicate that as water potential decreasesspore germination decreases. Theseresults suggest that spore viability mayvary with soil moisture, and sporegermination may occur at soil moisturelevels that are not optimal for plantroots. My data support previousobservations (Khan, 1972; Trinick,1977) that the amount of moistureinitially present in soil may affectmycorrhizal colonization of roots andthus the MIP of the soil. My data showa significant linear relationship (R 2 =0.996) between moisture initially presentin the soil and MIP. Colonization ofroots by VA mycorrhizal fungi decreaseswhen the amount of moisture initiallypresent in the soil increases. In spite ofthe highly significant relationship, I