GROWTH OF LITTLE BLUESTEM (SCHIZACHYRIUM SCOPARIUM) (POACEAE) IN FUMIGATED AND NONFUMIGATED SOILS UNDER VARIOUS INORGANIC NUTRIENT CONDITIONS

Little bluestem plants (Schizachyrium scoparium (Michx.) Nash) were grown in fumigated and nonfumigated soil under manipulated levels of three inorganic nutrients: nitrogen, phosphorus, or bases (Ca + Mg). Plants grown in nonfumigated soil had significantly (P < 0.05) higher tissue levels of inorganic nutrients (Cu, Zn, Al, S, Mg, Mn, Ca, and P), smaller shoots, less total biomass, fewer flowering plants but more VAM fungal colonization than plants grown in fumigated soil that were essentially nonmycorrhizal (colonization x ? S) = 34.4 ? 13.8% vs. 1.2 ? 4.9%, for plants grown in nonfumigated and fumigated soil, respectively). Levels of phosphorus (14-33 Ag/g) available (Bray No. 1) in the soil prior to manipulation, which are adequate for little bluestem, likely resulted in the development of an ineffectual mycorrhizal association, which in turn, caused the depressed growth of plants in nonfumigated soil. Among plants grown in nonfumigated soil, there was significant variation in VAM fungal colonization and sporulation owing to nutrient treatment. Nitrogen treatment and deionized water control had significantly lower levels of colonization than phosphorus and base treatments. However, plants in the nitrogen and base treatments had significantly more spores/ 100 cc of rhizosphere soil than plants grown in the deionized water control. MYCORRHIZAL PLANTS are often more competitive (E. Allen, 1982), contain higher levels of inorganic nutrients (Hayman, 1983; Hall, Johnstone, and Dolby, 1984), are more drought-resistant (M. Allen, 1982; Nelsen and Safir, 1982), and have higher photosynthetic rates (Allen et al., 1981) than nonmycorrhizal plants grown under the same conditions. These positive effects of the mycorrhizal association have generally been demonstrated under conditions where inorganic nutrients, especially phosphorus, were limiting (Safir and Duniway, 1982; Hayman, 1983). In some studies, the lack of a positive effect of mycorrhizae has been reported (Hays et al., 1982; Wallace, 1987). This response has been attributed to a variety of factors including root form of the host species (Baylis, 1970; Warner and Mosse, 1982), growth in partially sterilized soil (Baylis, 1975), and high availability of inorganic nutrients (Buwalda and Goh, 1982). Hays et al. (1982) reported that mycorrhizal blue grama grass (Bouteloua gracilis (H.B.K.) I Received for publication 20 January 1988; revision accepted 18 May 1988. We thank Dr. Gerald Gerloff, University of WisconsinMadison, for assistance in determining the amount and chemical form of the supplemental inorganic nutrients added in the various treatments, and the Illinois Department of Conservation for granting permission for our study. This work was supported by NSF Grant BSR 8420032. Lag. ex Steud.), a native North American shortgrass prairie species, experienced depressed growth compared to nonmycorrhizal plants grown under moderate to high levels of ammonium nitrogen (4-126 Ag/g) and moderate levels of phosphorus (3-22 Ag/g). These results suggest that studies of mycorrhizal response to inorganic nutrients should consider availability of nutrients in addition to phosphorus (Hall et al., 1984). We found significant correlations between abundance of mycorrhizal spores and plant cover and between these two parameters and soil moisture and various inorganic nutrients (Anderson, Liberta, and Dickman, 1984). However, because of multicollinearity associated with many variables we were unable to delineate separate influences of inorganic nutrients or soil moisture on VAM response. Others have approached similar problems by conducting experiments in pot-cultures under greenhouse conditions. But results from these studies may have limited application to ecological systems (St. John and Coleman, 1983). Ideally, the response of the association can be best understood within the context of a natural community where all of these variables operate in concert. The purpose of this study was to examine the growth and VAM fungal colonization of little bluestem grown in fumigated and nonfumigated prairie soil under varied inorganic nutrient conditions (nitrogen, phos-