Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)


Plant Science

First Advisor

C.J. Mankin


The mixed prairie association has a characteristic soil microfungal flora associated with the cover vegetation (Clarke and Christensen, 1980). Rhizosphere organisms are correlated with the cover vegetation (Christensen, 1969) and a change in the cover vegetation should be accompanied by a change in the organisms in the rhizosphere. Some disturbances that may lead to change in the cover vegetation are tillage, grazing, interseeding, mowing and fires. Christensen's (1980) review of species diversity and dominance in fungal communities indicates that in general these disturbances tend to reduce soil microfungal diversity while increasing the frequency of the remaining species. Other studies have shown that the soil microfungi demonstrate a succession that corresponds to the seral stages of the above ground plants as they progress from a pioneer to a climax vegetational unit (England and Rice, 1957; Brown, 1958; Wohlrab, et. al. 1963; Mallik and Rice, 1966; Gochenhour and Whittingham, 1967; Wallace and Dickensen, 1978; and Widden and Parkinson, 1979). In agricultural crops the microfungi associated with the roots of a developing crop are influenced by plant age, soil type, position in relation to the root (rhizoplane versus rhizosphere) and response to soil fungistasis - low sensitivity being correlated with pioneer colonization of the root and high sensitivity to secondary or non-colonization of the rhizoplane (Peterson, 1958; Das, 1963; Dix, 1967; Young and Kucharek, 1977; and Odunfa and Oso, 1979). Christensen (1980) analyzed key studies and concurs that these factors affect the diversity of species found in a developing community. In general as succession proceeds the community becomes more diverse and stable. There is disagreement, however, as to the linearity of these relationships. Louck's (1970) studies of general ecological theory indicate a wave pattern in relation to species diversity as succession carries the community toward a climax. Bazzaz (1975) also concluded that succession-diversity relationships are not linear and offered some explanations for the nonlinearity observed. He felt diversity is increased by vertical and horizontal microenvironmental heterogeneity, niche preemptation [sic] and sharing of community resources by species of intermediate importance values. Diversity is decreased through the production of allelopathic and other interference substances. The current study was undertaken to investigate the microfungal successional changes that occur in old wheat field soils reseeded to grass.

Library of Congress Subject Headings

Soil fungi
Soil microbiology
Grasslands -- South Dakota




South Dakota State University